Android PTPP VPN session stalling after precisely 30-31 minutes
Does the rest of the Internet work? Or is it just the Netflix service?

In any case, contact your VPN service provider for advise. As long as the VPN connection is not terminated (as you say it isn’t) any problem is likely to be much easier debugged on the service providers side. You have noticed a pattern, and that should be debuggable for them.