Hello,
While I can’t tell the exact cause, I can say that the issue appears to be within the traffic offloading layer on the TRB500.
If the modem firmware is not RG501QEUAAR12A08M4G_04.200.04.200, could you try updating using the process described here: TRB500 modem update proceedure
This modem firmware fixes the issues that were previously present with some operators utilizing n28 5G band, as well as some other improvements.
Additionally, it seems like you are using TRB500 in NAT mode with only a router connected downstream. If this is the case, I’d suggest setting the TRB500 to Bridge or Passthrough mode by navigating to Network → WAN → edit mob1s1a1 instance and change the mode to Passthrough (this most likely won’t help with the issue, but it will help avoid double or triple NATing).
Could you also comment what sort of configuration you have on the TRB500? Is it running any of the included services? Perhaps you have any custom mobile connection parameters?
Best regards,