Postie Test button (and others too) not responding

Hey, I configured Postie, I clicked the Test configuration button, a blank page shown and timed out.

In browser console I see ERR_HTTP2_PROTOCOL_ERROR 200, in server console. So the response code is 200, but the response itself seems corrupted/timed out.

In server logs I see:

82.113.48.11 - - [02/Mar/2023:14:23:17 +0100] "GET /wp-content/plugins/postie/icons/silver/default-32.png HTTP/2.0" 200 5473 "https://www.myweb.cz/wp-admin/admin.php?page=postie-settings" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.0.0 Safari/537.36"

37.205.12.187 - - [02/Mar/2023:14:23:23 +0100] "POST /wp-cron.php?doing_wp_cron=1677763403.8288159370422363281250 HTTP/1.1" 200 31 "https://www.myweb.cz/wp-cron.php?doing_wp_cron=1677763403.8288159370422363281250" "WordPress/6.1.1; https://www.myweb.cz"

==> www.myweb.cz.error.log <== 2023/03/02 14:23:23 [error] 531947#531947: *904572 FastCGI sent in stderr: "PHP message: Postie [debug]: enabling duplicate commentsPHP message: Postie [debug]: doing postie_session_startPHP message: Postie [debug]: Starting mail fetchPHP message: Postie [debug]: WordPress datetime: 2023-03-02 14:23:23PHP message: Postie [debug]: wp_content_path: /var/www/myweb.cz/wp-contentPHP message: Postie [debug]: OS: LinuxPHP message: Postie [debug]: PHP version: 8.0.28PHP message: Postie [debug]: PHP error_log: PHP message: Postie [debug]: PHP log_errors: OnPHP message: Postie [debug]: PHP get_temp_dir: /tmp/PHP message: Postie [debug]: PHP disable_functions: pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,pcntl_unshare,PHP message: Postie [debug]: PHP cURL version: 7.64.0PHP message: Postie [debug]: PHP Multibyte String support: yesPHP message: Postie [debug]: MySQL Version: 10.3.38PHP message: Postie [debug]: MySQL client: mysqliPHP message: Postie [debug]: Query: SHOW FULL COLUMNS FROM wp_postsPHP message: Postie [debug]: wp_posts charset: utf8mb4PHP message: Postie [debug]: WordPress Version: 6.1.1PHP message: Postie [debug]: WordPress MultisitePHP message: Postie [debug]: network_home_url(): https://www.myweb.cz/PHP message: Postie [debug]: WP_TEMP_DIR: (none)PHP message: Postie [debug]: WP_HOME: (none)PHP message: Postie [debug]: home_url(): https://www.myweb.czPHP message: Postie [debug]: WP_SITEURL: (none)PHP message: Postie [debug]: site_url(): https://www.myweb.czPHP message: Postie [debug]: WP_DEBUG: OffPHP message: Postie [debug]: WP_DEBUG_DISPLAY: OnPHP message: Postie [debug]: WP_DEBUG_LOG: OffPHP message: Postie [debug]: WP_MAX_MEMORY_LIMIT 2023/03/02 14:23:23 [error] 531947#531947: *904572 FastCGI sent in stderr: ": 3.7.0PHP message: Postie [debug]: gd version: PHP message: Postie [debug]: image editor supported: WP_Image_Editor_ImagickPHP message: Postie [debug]: WP_Image_Editor_Imagick supports: image/jpegPHP message: Postie [debug]: WP_Image_Editor_Imagick supports: image/pngPHP message: Postie [debug]: WP_Image_Editor_Imagick supports: image/gifPHP message: Postie [debug]: image editor not supported: WP_Image_Editor_GDPHP message: Postie [debug]: Registered image sizesPHP message: Postie [debug]: Array ( [0] => thumbnail
[1] => medium
[2] => medium_large
[3] => large
[4] => thumblist
[5] => meccarouselthumb
[6] => gridsquare
[7] => tileview
[8] => 1536x1536
[9] => 2048x2048
)
PHP message: Postie [debug]: No registered filters for image_downsizePHP message: Postie [debug]: No registered filters for wp_handle_uploadPHP message: Postie [debug]: No registered filters for wp_get_attachment_thumb_filePHP message: Postie [debug]: Registered filters for wp_handle_upload_prefilterPHP message: Postie [debug]: No registered filters for wp_handle_sideload_prefilterPHP message: Postie [debug]: No registered filters for pre_move_uploaded_filePHP message: Postie [debug]: image memory limit: 512MPHP message: Postie [debug]: DISABLE_WP_CRON: OffPHP message: Postie [debug]: ALTERNATE_WP_CRON: OffPHP message: Postie [debug]: WP_CRON_LOCK_TIMEOUT: 60PHP message: Postie [debug]: iconv: presentPHP message: Postie [debug]: Active pluginsPHP message: Postie [debug]: advanced-custom-fields/acf.php => 5.12.3PHP message: Postie [debug]: all-in-one-seo-pack/all_in_one_seo_pack.php => 4.2.5.1PHP message: Postie [debug]: better-font-awesome/better-font-awesome.php => 2.0.3PHP message: Postie [debug]: block-visibility/block-visibility.php => 2.4.3PHP message: Postie [debug]: check-" while reading upstream, client: 82.113.48.11, server: myweb.cz, request: "POST /wp-admin/admin.php?page=postie-settings
2023/03/02 14:23:23 [error] 531947#531947: *904572 FastCGI sent in stderr: "email/check-email.php => 1.0.6PHP message: Postie [debug]: cookie-notice/cookie-notice.php => 2.4.0PHP message: Postie [debug]: custom-post-type-ui/custom-post-type-ui.php => 1.13.1PHP message: Postie [debug]: enable-media-replace/enable-media-replace.php => 4.0.0" while reading upstream, client: 82.113.48.11, server: myweb.cz, request: "POST /wp-admin/admin.php?page=postie-settings HTTP/2.0", upstream: "fastcgi://unix:/var/run/php/php8.0-fpm.sock:", host: "www.myweb.cz", referrer: "https://www.myweb.cz/wp-admin/admin.php?page=postie-settings"
2023/03/02 14:23:23 [error] 531947#531947: *904572 FastCGI sent in stderr: "PHP message: Postie [debug]: gallery-block-lightbox/gallery-block-lightbox.php => 1.11PHP message: Postie [debug]: google-site-kit/google-site-kit.php => 1.83.0PHP message: Postie [debug]: insert-pages/insert-pages.php => 3.7.4PHP message: Postie [debug]: limit-login-attempts-reloaded/limit-login-attempts-reloaded.php => 2.25.5PHP message: Postie [debug]: mec-fluent-layouts/mec-fluent-layouts.php => 1.2.6PHP message: Postie [debug]: media-file-renamer/media-file-renamer.php => 5.4.4PHP message: Postie [debug]: members/members.php => 3.2.1PHP message: Postie [debug]: modern-events-calendar-lite/modern-events-calendar-lite.php => 6.5.6PHP message: Postie [debug]: no-self-ping/no-self-pings.php => 1.1.5PHP message: Postie [debug]: myweb/myweb.php => 0.1.0PHP message: Postie [debug]: postie/postie.php => 1.9.65PHP message: Postie [debug]: redirection/redirection.php => 5.3.3PHP message: Postie [debug]: restrict-user-access/restrict-user-access.php => 2.4PHP message: Postie [debug]: show-current-template/show-current-template.php => 0.4.6PHP message: Postie [debug]: simple-post-notes/simple-post-notes.php => 1.7.6PHP message: Postie [debug]: slide-anything/slide-anything.php => 2.4.6PHP message: Postie [debug]: wp-mail-smtp-mailer/wp-mail-smtp-mailer.php => 1.0.7PHP message: Postie [debug]: wp-statistics/wp-statistics.php => 13.2.6PHP message: Postie [debug]: Postie is in /var/www/myweb.cz/wp-content/plugins/postie/PHP message: Postie [debug]: Postie Version: 1.9.65PHP message: Postie [debug]: POSTIE_DEBUG: OnPHP message: Postie [debug]: No registered filters for postie_filter_emailPHP message: Postie [debug]: No registered filters for postie_filter_email2PHP message: Postie [debug]: No registered filters for postie_filter_email3PHP message: Postie [debug]: No regis" while reading upstream, client: 82.113.48.11, server: myweb.cz, request:
2023/03/02 14:23:23 [error] 531947#531947: *904572 FastCGI sent in stderr: "tered filters for postie_authorPHP message: Postie [debug]: No registered filters for postie_post_beforePHP message: Postie [debug]: No registered filters for postie_post_afterPHP message: Postie [debug]: No registered filters for postie_file_addedPHP message: Postie [debug]: No registered filters for postie_galleryPHP message: Postie [debug]: No registered filters for postie_comment_beforePHP message: Postie [debug]: No registered filters for postie_comment_afterPHP message: Postie [debug]: No registered filters for postie_category_defaultPHP message: Postie [debug]: Registered filters for postie_log_debugPHP message: Postie [debug]: Registered filters for postie_log_errorPHP message: Postie [debug]: No registered filters for postie_session_startPHP message: Postie [debug]: No registered filters for postie_session_endPHP message: Postie [debug]: No registered filters for postie_preconnectPHP message: Postie [debug]: No registered filters for postie_post_prePHP message: Postie [debug]: No registered filters for postie_email_reject_recipientsPHP message: Postie [debug]: No registered filters for postie_email_notify_recipientsPHP message: Postie [debug]: No registered filters for postie_email_reject_subjectPHP message: Postie [debug]: No registered filters for postie_email_notify_subjectPHP message: Postie [debug]: No registered filters for postie_email_reject_bodyPHP message: Postie [debug]: No registered filters for postie_place_mediaPHP message: Postie [debug]: No registered filters for postie_place_media_beforePHP message: Postie [debug]: No registered filters for postie_place_media_afterPHP message: Postie [debug]: No registered filters for postie_rawPHP message: Postie [debug]: No registered filters for postie_bare_linkPHP message: Postie [debug]: No registered filters for postie_categoryPHP message: Post" while reading upstream, client: 82.113.48.11, server: myweb.cz, request: "POST /wp-admin/admin.php?page=postie-settings
2023/03/02 14:23:23 [error] 531947#531947: *904572 FastCGI sent in stderr: "ie [debug]: No registered filters for postie_file_added_prePHP message: Postie [debug]: No registered filters for postie_include_attachmentPHP message: Postie [debug]: default_charset: UTF-8PHP message: Postie [debug]: DB_CHARSET: utf8PHP message: Postie [debug]: DB_COLLATE: database defaultPHP message: Postie [debug]: WordPress encoding: UTF-8PHP message: Postie [debug]: memory at start of email processing: 29334416PHP message: Postie [debug]: postie configuration" while reading upstream, client: 82.113.48.11, server: myweb.cz, request: "POST /wp-admin/admin.php?page=postie-settings HTTP/2.0", upstream: "fastcgi://unix:/var/run/php/php8.0-fpm.sock:", host: "www.myweb.cz", referrer: "https://www.myweb.cz/wp-admin/admin.php?page=postie-settings"