Admin Area Inaccessible when QSM plugin is active – fix

Moving my issues to a new thread for ease of following –

Site admin became inaccessible two days ago. By looking at error logs and selectively deactivating plugins using File Manager, I determined the issue was a conflict with QSM ver 6.3.2 that seems to only affect the Admin. The public side of the website was working correctly, even when the QSM plugin is active and the Admin was inaccessible.

Error page info (below) also mentions Endurance Cache – a “must use” plugin installed by the hosting provider (GreenGeeks).

I discovered that by disabling the Endurance Cache must-use (MU) plugin(s) — Endurance Browser Cache v 0.2 and Endurance Page Cache v 0.4 — I can then re-enable QSM and the Admin remains functional.

Posting this in case it might help someone else.

To restate the fix: disable the QSM plugin by renaming the plugin folder. Regain access to the Admin. Disable the Endurance plugins, then re-activate the QSM plugin. The Endurance plugins are loose php files in the wp-content/mu-plugins/ folder, and I wasn’t sure if it was safe to move or rename the php files. They can be disabled within the plugins area of the Admin.

Fatal error: Uncaught Error: Call to a member function get_year_permastruct() on null in /home/acucurre/public_html/wp-includes/link-template.php:475 Stack trace: #0 /home/acucurre/public_html/wp-content/mu-plugins/endurance-page-cache.php(83): get_year_link('2019') #1 /home/acucurre/public_html/wp-includes/class-wp-hook.php(288): Endurance_Page_Cache->save_post(14549) #2 /home/acucurre/public_html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array) #3 /home/acucurre/public_html/wp-includes/plugin.php(465): WP_Hook->do_action(Array) #4 /home/acucurre/public_html/wp-includes/post.php(3951): do_action('save_post', 14549, Object(WP_Post), false) #5 /home/acucurre/public_html/wp-content/plugins/quiz-master-next/php/classes/class-qmn-log-manager.php(128): wp_insert_post(Array) #6 /home/acucurre/public_html/wp-content/plugins/quiz-master-next/php/classes/class-qmn-log-manager.php(104): QMN_Log_Manager->insert_log(Array) #7 /home/acucurre/public_html/wp-content/plugins/quiz-master-next/php/classes/class-qsm-t in /home/acucurre/public_html/wp-includes/link-template.php on line 475