ldd-directory-lite/includes/cmb/includes/CMB2_Hookup.php

Reverting to the previous version of the plugin fixed the issue.

Same here – fortunately, had a backup ready to hand. I didn’t have debug turned on, but was simply unable to log into admin. Once I turned on debug, I got the messages. Here are the lot:

Warning: include_once(/var/www/html/testsite/wp-content/plugins/ldd-directory-lite/includes/cmb/includes/CMB2_Hookup.php): Failed to open stream: No such file or directory in /var/www/html/testsite/wp-content/plugins/ldd-directory-lite/includes/cmb/includes/helper-functions.php on line 44

Warning: include_once(): Failed opening '/var/www/html/testsite/wp-content/plugins/ldd-directory-lite/includes/cmb/includes/CMB2_Hookup.php' for inclusion (include_path='.:/usr/share/php') in /var/www/html/testsite/wp-content/plugins/ldd-directory-lite/includes/cmb/includes/helper-functions.php on line 44

Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, class "CMB2_Hookup" not found in /var/www/html/testsite/wp-includes/class-wp-hook.php:307 Stack trace: #0 /var/www/html/testsite/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #1 /var/www/html/testsite/wp-includes/plugin.php(476): WP_Hook->do_action() #2 /var/www/html/testsite/wp-content/plugins/ldd-directory-lite/includes/cmb/bootstrap.php(75): do_action() #3 /var/www/html/testsite/wp-content/plugins/ldd-directory-lite/includes/cmb/init.php(165): cmb2_bootstrap() #4 /var/www/html/testsite/wp-includes/class-wp-hook.php(307): CMB2_Bootstrap_2101->include_cmb() #5 /var/www/html/testsite/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #6 /var/www/html/testsite/wp-includes/plugin.php(476): WP_Hook->do_action() #7 /var/www/html/testsite/wp-settings.php(598): do_action() #8 /var/www/html/testsite/wp-config.php(92): require_once('...') #9 /var/www/html/testsite/wp-load.php(50): require_once('...') #10 /var/www/html/testsite/wp-admin/admin.php(34): require_once('...') #11 /var/www/html/testsite/wp-admin/index.php(10): require_once('...') #12 {main} thrown in /var/www/html/testsite/wp-includes/class-wp-hook.php on line 307

For anyone who gets caught out and needs the earlier versions you can download it by going to the https://www.ads-software.com/plugins/ldd-directory-lite/ and click Advanced View (the link on the right hand side) then scroll down to the bottom you can select a version to download.