To be clear, my situation was never exactly as you describe. I’ve never had trouble with the initial router to modem connection, but it was not stable. Sometimes it would last 30 seconds. Sometimes it would last a few hours. I am using an Arris modem now, but it was the same with a Netgear. Reference Rick’s comment above, my situation is also only on Comcast.
I’ve had the Balance One running on 7.1.1b2 for 72 hours with no interruptions. I haven’t done any speed tests because I don’t have a benchmark from before, but the connection feels quicker. My WAN settings are 1Gbps full duplex, advertised speed is UN-checked.
I am changing the WAN settings to Auto now, and will report back in a couple days if there is any difference. Ideally it should not be necessary to use anything other than Auto.
Specifically with reference to Comcast, I have found their DNS servers to be unreliable. I’ve fixed several other Comcast installations by changing the DNS to public servers such as 126.96.36.199 and 188.8.131.52. Those other installations did not include a Peplink device. On the Balance be sure to UN-check “acquire DNS server address automatically.”