For the filament sensor problem , here are some suggestions for reference .
1. Make both extruders loaded even just print with one extruder.
Otherwise , the machine will show this error .
2. Check if the plugs of filament sensors are come to loose.
3. Check if the plug at this place is come to loose.
4.If all above checked but still makes no sense , it is possibly that the filament sensor is broken and need a replacement you may contact with supportor : firstname.lastname@example.org .