I have pretty much the same issues as previous users.
WAN 1 is TW Roadrunner Business.
WAN 2 is a T1.
I get a FAILED WAN DNS on WAN1 almost weekly. Got TW out there to troubleshoot their modem and they replaced but I still have the same issues. I tried disconecting and reconnecting via the web interface to no avail. However, I can ping the modem interface (external) all day long. The only remedy is to reboot the Peplink Balance 20. Here are my unit details: Peplink Balance 20
5.3.12 build 1303