There are a number of possible scenarios where network can refuse the mobile the requested service. See At commands AT+QEMMTIMER, specifically for backoff_timerID = 5, T3396.
If network rejects the device because of network loading or other reason, the device can stay offline for about 12 minutes at a time. Restarting the module whilst this timer is active only restarts this 12 minute timer again. So use this command to check if this network reject timer is active. If so then DO NOT restart the module. Technically in 3GPP it is called the T3396 backoff timer, see the reference below: