Strange server unreachable - php?

I have a strange issue and don’t know where to turn. A little over a year ago I’d need to restart php-fpm on occasion or the server would become unreachable. I had setup monit to watch for the issue and restart the problem php version. After a Hestia update (I have no idea which one) Monit stopped reporting the issue and the failures disappeared from the logs. But fairly regularly the same issue comes up, but I can’t see in the logs what the cause is. It resolves itself after about 30 seconds.
I’m pretty sure this has to do with php (because sites on php8 will still be active if php7.4 is down and vice a versa.
Can anyone suggest why and/or a solution.