I got this error while adding topics from the front page.
Hi @netvilox,
Do you have some JS optimizer plugin? Please deactivate all Optimizer and Minifier plugins, delete all cache and test it again.
Don't forget to press Ctrl+F5 (twice) on frontend before checking to reload updated JS/CSS files. If you check it on mobile browser check on incognito mode.
PLEASE do not take my advice the wrong way. Having said that, you seem to use PHP 5.6 and that is OLD and discontinued. Maybe some problems come from that. Also you may have an OLD database for mysql.
And i see you always add new things. Don't.
Stabilize your system first, be sure everything works, and then add things ONE at a time.
You should update your PHP to at least 7.x or later if you can. Same for mysql db (if old).
Then see if the problem is solved.
If not, then follow the standard WP debug. Disable plugins, enable debug to a log, etc etc. We have posted all that several times, also available on the net, no need to repeat them.