Aborted connection # to db: 'pi' user: 'pi' host: 'localhost' (Got an error reading communication packets)

Hi,
I see these errors in the MySQL error log file, every 5 minutes it says about Aborted connection to DB.

2020-10-06T08:00:03.367510Z 1684 [Note] Aborted connection 1684 to db: ‘pi’ user: ‘pi’ host: ‘localhost’ (Got an error reading communication packets)
2020-10-06T08:05:03.178929Z 1685 [Note] Aborted connection 1685 to db: ‘pi’ user: ‘pi’ host: ‘localhost’ (Got an error reading communication packets)

I’ve tried to increase max_allowed_packet=256M but it doesn’t help.
This error occurs on 3.3 and 3.4 PrivacyIDEA versions, there are NO issues on UI.
I’m not an expert on MySQL, I would appreciate if someone explains the reason of those errors.
Thanks.