Hello,
In this case, I'd recommend factory resetting the device, enabling the WAN access, and trying to access it from the WAN. There are no issues reported with this feature, so the issue is most likely somewhere in the network.
You could also try using different devices to access the RUT, clearing the browser cache, etc.
Also, by my last question, I meant does the port forwarding work from WAN to LAN? Can you reach the LAN devices from your private mobile network after setting up port forwarding?
Best regards,
DaumantasG