Class ” ” not found error

Last week, some time after updating to UM 2.12.0, we had over 400 instances of the error pasted below in our log. The fatal error alert email identified at least one page where the error was caught. By the time we checked the site, everything was working normally, and there does not seem to be anything unusual on the identified page.

The error has not recurred, but some time the following day, another plugin (ACF) apparently deactivated itself, with nothing in the log to indicate why it did so. We do not know whether or not this was connected to the UM issue.

We’d like to know why this happened and what, if anything, we need to do to prevent a recurrence. Thanks in advance.

[18-Jun-2026 02:32:07 UTC] PHP Fatal error:  Uncaught Error: Class "" not found in /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/core/class-files.php:16
Stack trace:
#0 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(356): include_once()
#1 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(1182): UM->um__autoloader('um\\core\\class-f...')
#2 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(509): UM->files()
#3 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(198): UM->includes()
#4 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(96): UM->_um_construct()
#5 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(1441): UM::instance()
#6 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/class-init.php(1446): UM()
#7 /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/ultimate-member.php(43): require_once('/home/concerti/...')
#8 /home/concerti/public_html/wordpress/wp-settings.php(589): include_once('/home/concerti/...')
#9 /home/concerti/public_html/wordpress/wp-config.php(94): require_once('/home/concerti/...')
#10 /home/concerti/public_html/wordpress/wp-load.php(50): require_once('/home/concerti/...')
#11 /home/concerti/public_html/wordpress/wp-blog-header.php(13): require_once('/home/concerti/...')
#12 /home/concerti/public_html/index.php(17): require('/home/concerti/...')
#13 {main}
  thrown in /home/concerti/public_html/wordpress/wp-content/plugins/ultimate-member/includes/core/class-files.php on line 16