I found some weirdness today and for the last hour or so the problem is gone! Here's all I did:

- I put the game into full screen mode (not borderless window), applied with correct resolution to monitor
- I then returned the game to full screen borderless windows mode, applied

No issue for an hour!

Fingers crossed. Maybe it reset some weird configuration file that was off?

I don't think the port forward will change anything. I play on my laptop behind the same firewall without the issue