We had a similar problem with one of our warehouse locations after switching to AT&T Business Fiber. IPsec site to site VPN to our head office would randomly stop passing traffic, traffic outside the tunnel was fine. For us, the issue was fixed by disabling ESP ALG on the AT&T gateway.

I was having similar issues with this the week of 04/22/2020, with the chicago3.voip.ms server. This was shortly after they added new servers in Chicago. I switched everything to chicago7.voip.ms and have had no issues since.

We had a similar problem with one of our warehouse locations after switching to AT&T Business Fiber. IPsec site to site VPN to our head office would randomly stop passing traffic, traffic outside the tunnel was fine. For us, the issue was fixed by disabling ESP ALG on the AT&T gateway.