XF 2.1 strange problem

[gouwepeer.nl]

My forum has a strange problem:
The forum starts to slow down for no reason, the forum keeps loading, it takes forever to give a like and logged out members can no longer log in.
My host's server automatically creates backups. After restoring a backup (files only, database can remain unchanged) from a few days ago, (and after upgrading to the newest version) everything works super fast again. After a few weeks, the problem starts again.
After posting a message, the message will appear in the forum, but it will also remain in the input box.
An existing message cannot be edited again, it simply will not open. Same time smileys from the menu cannot be added either.

Forum version: v2.1.8 Patch 2
PHP version: 7.3.15
MySQL versie: 10.1.44 (10.1.44-MariaDB-cll-lve)

 

[gouwepeer.nl]

It look likes a overlay loading problem. The file overlay.php is unchanged.
I have a containerized (shared) hosting, 1GB RAM and 1 cpu core, 128mb Redis Cache, unlimited SSD storage (fair use policy), unlimited data traffic, no errors in my XF logbook.

 

[gouwepeer.nl]

The problem is back (again).
It appears to be after a "one click upgrade".
I am now going to restore a backup and then manually upgrade.

 

[gouwepeer.nl]

And it's back again

 

[gouwepeer.nl]

Problem solved