No, there is not documented troubleshoot process, but the idea in this case is as follows:
1. First it is essential to check if device can determine its GPS location. Connect to this router's WebUI and check if in "Services -> GPS -> Map" menu correct GPS location is shown. Also, as "setuid" user commented above, through SSH/CLI more information can be seen. Connect to device via SSH (e.g. using "Putty" application for Windows):
- SSH login: root
- SSH password: <your device's password>
and use "gpsctl -p" SSH command to check how much satellites router can see at that moment in time. If number is low, that would explain inaccuracy or loss of GPS position. If this would be the case, situation could only by improved by physically changing your setup, e.g. changing GPS antenna location. If possible, make sure that it would have direct sky visibility and would not have any obstructions between it and the sky.
2. If we understood you correctly, you have also configured router to send its location to your servers, either via RAW NMEA, HTTP or AVL functionalities. If this is the case, it is also possible that device looses internet connection temporarily, which prevents it from reporting new GPS position to your server. If you are using mobile internet connection with your routers and if they receive poor mobile signal coverage, try to change LTE antenna location and place them closed to the window/higher if possible.