"Your connection seems to be closed"

So I occasionally have this problem where my players cannot connect to my Foundry client. The pic below shows the only indicator foundry gives of the problem. im on [D&D5e] and V10 if that matters.

https://preview.redd.it/1rbpc8p7tsfb1.jpg?width=402&format=pjpg&auto=webp&s=bd7600babc90fcbdb16536733cddd50b9955ad8c

This problem began about two months ago and I have no idea why. We've played for over a year without this issue. Now for some reason for days at a time my players can't connect.

I am able to connect from the local network address on the local network, from the same pc and others.

My firewall settings are not causing this because they have not changed between now and the last time that they were able to get connected.

I have tried checking and unchecking UPnP. And I have even tried getting my friends to connect while running on a VPN service and to no avail.

My router is not port forwarded because the Xfinity router I have does not allow it for some reason but UPnP has worked FOR OVER A YEAR and it randomly wont for one to three days. So that's the only thing I can think is that maybe some how my ISP is to blame? If anyone has any info or insight it would be greatly appreciated. If nobody has experienced this I guess my next step is going to be buying a router I can port forward but I'm concerned that wont solve my problem.