In fact, we are not using gsm/gprs features, just fcm one. We are switching modes in order to change baud rate.
It worths note that in some test scenarios, with baud rate changing not so oftenly, the flow is not closed and module keeps running steadly (changing baud rate from 600 to 9600, and then back to 600) for hours. But if we change the pattern of messages sent by/to the FCM, we end up in this situation (fcm closed).
We are running tests with a modified version, that re-opens FCM in case a FLOW_CLOSED event is received.
However, it will be insightful to know what is the cause of such behaviour.