Hi,
1. Check if your antennas are attached tightly and not loose.
2. Check if your signal is at least about -80, if not - check antennas again and that your router is not somewhere where it could block the signal.
3. Reset your router to default factory settings and set it up again, use Custom APN given by your operator.
4. Check if other operator SIM cards behave the same.
EB.