Matomo server down

We have quite a lot of traffic at the moment and our server with Matomo is always going down. To solve the problem the hoster told me he had to increase “pm.max_children” to 20 which only helped for a short time. Now I keep increasing this value but I anyway get a 504 error after a while.

When checking the system check I saw this:
Num invalidations 56 queued, 19 in progress

Might this be the problem? We run a CRON job every hour that does the archiving.

Any idea what to try? System check shows no issues except “LOAD DATA INFILE” which the hoster can’t chease because of security reasons.