help debug mysql problem

Job ID: 33957077

Budget: €30 – €250 EUR

Hello mysql / mariadb experts

I'm using mariadb 10
on debian 10 (buster)

on a busy application that does a lot of queries
on a rather large table (between 5M and 20M rows, depending on the server)
with a lot of indexes.

I have a page that performs around 10K updates on this table
and when there are other concurrent jobs,
I get random sql errors.

The query is valid,
the hardware (ram) should be enough,
the cpu usage is reasonable
and I get no errors from the server, I can't find anything in the logs:
no kernel limits have been reached, no crashes.

It's a strange problem and I need some help to track this down.

Please bid only if you are a mysql 'guru'.

Max 100 euros.

Thank you.