Latest WordPress upgrade breaks this plugin for multi-user sites in mu-plugins

Links to suburb meeting lists are broken yielding

No Meetings Found

Or

Internet or Server Problem

https://bmlt.naminnesota.org/main_server/

Please try again or contact your BMLT Administrator

Fatal error: Uncaught Error: Call to undefined function is_user_logged_in() in /home1/naminnes/public_html/naminnesota/wp-content/mu-plugins/endurance-page-cache.php:457 Stack trace: #0 /home1/naminnes/public_html/naminnesota/wp-content/mu-plugins/endurance-page-cache.php(490): Endurance_Page_Cache->is_cachable() #1 /home1/naminnes/public_html/naminnesota/wp-includes/class-wp-hook.php(286): Endurance_Page_Cache->finish(”) #2 /home1/naminnes/public_html/naminnesota/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array) #3 /home1/naminnes/public_html/naminnesota/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #4 /home1/naminnes/public_html/naminnesota/wp-includes/load.php(684): do_action(‘shutdown’) #5 [internal function]: shutdown_action_hook() #6 {main} thrown in /home1/naminnes/public_html/naminnesota/wp-content/mu-plugins/endurance-page-cache.php on line 457

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