The screenshots show WebUI of some MultiTech access point device.
As for the RUT240, could you navigate to Network -> Mobile and select Connection type as QMI?
If it does not help, or for some reason you specifically need to use PPP, it would be helpful if you could provide a troubleshoot file after the link goes down. To get the file, access router's WebUI, go to System -> Administration > Troubleshoot section and download troubleshoot file from there. The logs may provide more details about the cause of the issue.