Member List - fatal error

[STM1993]

Going to Member List leads to a white page with an error message.

EDIT:
Tested on Mozilla Firefox, both PC and Android.
Only while logged in, but not while logged out.

Code:

Fatal error: Uncaught Error: Call to undefined method DOMText::removeAttribute() in /www/htdocs/w019da8c/html/forum/inc/plugins/phoenixmasterplugin.php:291 Stack trace: #0 /www/htdocs/w019da8c/html/forum/inc/class_plugins.php(142): memberlist_show_bots('') #1 /www/htdocs/w019da8c/html/forum/memberlist.php(521): pluginSystem->run_hooks(Array) #2 {main} thrown in /www/htdocs/w019da8c/html/forum/inc/plugins/phoenixmasterplugin.php on line 291