It is difficult to estimate, what could be the reason for your issues.
Could you explain, or provide a screenshot, when the error "Profile in Use - Default" is displayed?
Also, when travelling, could you try setting up operator connections manually? This can be done by logging to the router's WebUI, navigating to Network -> Mobile -> Network Operators. Set Connection mode option to Manual or Manual - Auto and scan for available operators.
If the above does not solve your issue, I would like you to attach a troubleshoot file to your question. Please, replicate the issue, make sure the device is unable to provide internet access, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. The logs in the file might provide more insight into the issue.