I will try to reset to factory default. But really, when PPPoE, the main connection is lost and 3G/LTE is activated, the router cannot back to main connection.

Tony Seaford wrote As I know, this problem has been fixed. What's the model number? How about hardware version and firmware version of it? Firmware Version: 3.17.1 Build 140929 Rel.40245n Hardware...

I'm having exactly same problem. My main connection is WAN and 4G is backup. I set Wan with dynamic IP mode and then I try Wan PPPoE mode, and same problem. When WAN fails, 4G is activated and...