@Kartoff just to test if that is part of the problem but it isn't.
new development:
It seems the problem is on the side of PIA. I have added a gateway group and set it up to use PIA and NordVPN as a fallback and now it is running on NordVPN without a problem.
Another thread on this forum suggested that some PIA users are using the service to spam this very forum which is why some IPs seem to be banned. My humble attempt of an explanation is this: It seems reasonable to assume that PIA is having server issues and their servers are going down due to excessive load from spam activities. If the server that I am connected to is going down, then my connection would go down with it and not recover.