Hello, this was probably caused by the plug-in for calculating online time spent on the forum, which was available for the older version of the forum.
At this point it was deleted, the logs were cleared, I installed a new application working on the same principle for the current version of the forum, and what's left to wait is if the logs will appear again, so for now everything is fine, if something is wrong, I will contact you, thank you for quick response. Best regards