The issue is linked to modem module, not bootloader.
How long have you been using the device, did it work without issues previously?
Did you make any configuration changes, or did the device just randomly started to show this error?
It might be that you will need to return the device for warranty repair, but before that I would like to take a look at a troubleshoot file from your RUT955. To generate the file, access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. Attach it by editing your question.