We recently ran into an issue with poor connectivity where the module never was able to establish a TCP Connection.
- HL8548 reported it was attached. Our SIM Portal said otherwise (did not attach for 24 hours as we made sure it could not get signal)
- RSSI Readings appeared valid (did not verify it changed at all)
- Calling Detach and then Attach again resulted in a successful attach response. Again, the SIM portal did not indicate the radio ever attached since the last time over 24 hours prior.
- TCP Connection still failed
The only way to recover at that point was to hard reset the module.
This seems like a bug in the HL8548 running the RHL85xx.220.127.116.11.201610311418.x6250_7 version of the firmware that it lost its mind with regards to connection.