Problems when connecting x2 PPPOE connections simultaneously

Good day,

Ive been trying to solve a problem with our PEPLINK Balance 20 for a while now.
The modem is currently configured in two different modes on two WAN interfaces:

-> The 1st Interface is set to dial PPPOE from the peplink. The external modem is set to bridge mode, and all connectivity works just fine.
-> The 2nd WAN interface is set to NAT traffic between the external DLINK modem, which dials the actual connection. (DHCP Mode)
When this configuration is set, everything works perfectly.

The problem:
When I set both WAN interfaces to dial a PPPOE connection from the peplink itself (with both the external routers in bridge mode), the internet cannot be reached through either interfaces, however both state they are connected.

Pings go through but browsing websites does not work or are extremely slow.
Could this be a DNS issue? All ips seem to resolve just fine.
Is it safe to attach my config file?

Thanks for your help in advance


Thank you for the information provided thus far. If you could send the config file to support@peplink. We will diagnose from there.