strange memory_limit problem unsolveable when membership 2 pro combined with redis object cache

We have a strange issue within our default setup including a simple redis object-cache Plugin.
If we edit in Backend->Membership2->Settings->payments->stripe-single-gateway:
Our settings are sandbox and we change the value for Vendor Logo (i.e. want to save empty field) we get an neverending loading resulting in an memorylimit for every page until we flush the redis-cache.
it is reproduceable if we save the value "1 whitespace" and after that trying again saving an empty Vendor Logo field -> Neverending loading.

In the same time the redis-Cache has a max size of about 10-20MB while for php-fpm it makes no difference if we give eh memory_limit for php of 200,500 or 1000MB... Always returning an memory_limit issue.
If we deactivate the redis object-cache plugin we have no problem. So perhaps there is a loop or missuse of wordpress cache-functions. after running in this problem its no matter which url we try to request - everyone is running in the memory_limit error.