1- I have two devices with identical configuration and the Health Check disconnect happens on both.
2- ATT swapped their modem to a new one and it did not do anything.
3- I’ve contacted ATT support multiple times and did not get far with them. Except once they flashed settings from my modem under pretext of resetting it, which resulted in my longest outage (3-4 hours). Tech that showed up asked me to help him to recover it since his claim was “… I am not trained on this product”.
4- What DNSs are you using for Health Check ping? Comcast DNSs are not reliable, that’s why I’ve added 220.127.116.11
5- Is there correlation between HC disconnects and amount of consumed bandwidth?
6- To troubleshoot ISP connection, I would run mtr https://en.wikipedia.org/wiki/MTR_(software) outside of Peplink to get a picture of packet loss and latency when plugged directly to Comcast device.