TL-R480T+ disconnects WAN connection
I've got 2 WANs
WAN1: WiFi via CPE (Rebranded Ubitity CPE) - DHCP
WAN2: 3G/4G via Mobile Router (Netgear LB2120) - Static IP
Both directly connected to the TL-R480 setup to load balance and in the policy routing both WAN1 and WAN2 are on for all Service types and all Source and Destination IPs
For some reason the TL-R480 disconnects WAN after a time (especially during low usage periods, although I do have a constant ping setup to both the CPE on WAN1 and the mobile router on WAN2) ie shows as "Link Down" on "Connection Status" in the "System Status" page and in the Network -> WAN -WAN2 page Connection Status shows as "Disconnected" and Default Gateway, Primary DNS and Secondary DNS all show as 0.0.0.0.
If I click "Save" on this page it magically reconnects and data starts getting shared between each connection.
On the "Online Detection" in the "Load Balancing" I have tried setting WAN2 to "Always Online" but the Router for some reasons disconnects WAN2 and will only reconnect if you click "Save" on the Network -> WAN -WAN2 page (BTW whilst it's disconnected I can confirm that the Mobile Router on WAN2 does still have a connection).
What setting am I missing to prevent the TL-480T+ from disconnecting WAN2?
Oh I also tried swapping WAN2 and WAN1 settings, it just started disconnecting WAN1 instead.