The issue occurred after updating the page to Moodle 4.0.4.
When trying to find a user in "Potential user" box, receive this error (System Administrator > User > Assign System Roles):
Unexpected token '<', "<!doctype "... is not valid JSON
SyntaxError: Unexpected token '<', "<!doctype "... is not valid JSON
at JSON.parse (<anonymous>)
at Y.namespace.parse (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:24483:18)
at Object.handle_response (https://mysite/lib/javascript.php/1664186351/user/selector/module.js:9:56)
at Y.Subscriber._notify (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:13680:35)
at Y.Subscriber.notify (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:13709:24)
at Y.CustomEvent._notify (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:13372:17)
at Y.CustomEvent._procSubs (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:13498:36)
at Y.CustomEvent.fireSimple (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:13465:18)
at Y.CustomEvent._fire (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:13447:29)
at IO.fire (https://mysite/theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple.js:14600:22)Would you please help to resolve this issue?