I made some test to the automatic release of IP addresses by the network.
With the “Tuino096 - Quectel BG96” I attached to the network with the following AT commands:
As a Telekom employee I am in the lucky situation that I can check the IP status of the device via some monitoring systems. Of cause I could see that the my device with its IMEI and IMSI got assigned the IP address 10.0.4.102.
After this I just unplucked my device from power and checked the IP connection status of the IMEI.
It took about ca. 2 hours the DCD of the network recognized that the device is dead and release the IP address to be used again by other devices.
I repeated this test a few times and I could reproduce the 2 hours.
BUT if I power up the device after I swiched it off and attach it bag to the network the network detects the same IMEI and IMSI requires a new IP. By this the provious IP is released immediately and a new IP is assigned to the device.
Hope this info helps you a bit to get a better understanding what is going on in the network.