Same here. Tested last week after update to 6.3.0 in development environments we got these errors and warnings.
Uploading jpg or txt files is not working on front-end, the ticket on client side.
Trying to answer and upload files from admin side we got:
PHP Notice: Undefined variable: wp_filesystem in /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/file-uploader/class-file-uploader.php on line 2129
PHP Fatal error: Uncaught Error: Call to a member function move() on null in /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/file-uploader/class-file-uploader.php:2129
Stack trace: #0 /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/file-uploader/class-file-uploader.php(2048): WPAS_File_Upload->process_ajax_upload()
#1 /var/www/clients/client1/web100/web/wp-includes/class-wp-hook.php(324): WPAS_File_Upload->new_reply_ajax_attachments()
#2 /var/www/clients/client1/web100/web/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#3 /var/www/clients/client1/web100/web/wp-includes/plugin.php(517): WP_Hook->do_action()
#4 /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/functions-post.php(1136): do_action()
#5 /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/functions-post.php(672): wpas_insert_reply()
#6 /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/admin/functions-p in /var/www/clients/client1/web100/web/wp-content/plugins/awesome-support/includes/file-uploader/class-file-uploader.php on line 2129
In PHP errors log we see these errors that may not be related, but just in case…
PHP Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 262144 bytes) in /var/www/clients/client1/web100/web/wp-includes/class-wp-user.php on line 782
PHP Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 262144 bytes) in /var/www/clients/client1/web100/web/wp-includes/class-wp-object-cache.php on line 364