"PHP Error: Class 'ReflectionMethod' not found" since update to Nextcoud 14.1

Hello and sorry if it has already been answered but I couldn’t find anything about this error,

So I updated to Nextcloud 14.1 on monday, and ever since i’m getting =
“Error: Class ‘ReflectionMethod’ not found at /var/www/nextcloud/lib/private/AppFramework/Utility/ControllerMethodReflector.php#47” almost every 5 minutes, someties 4, sometimes 6.

I checked if the file was missing, but it is not, at the exact location.
I checked permissions, it’s all good.

Any Idea what to check next ?

Thanks a lot.