Also please include information:
1. was such situation happening for your devices from the very start when you started using them?
2. Are there devices among your FMA120 batch which work as expected ? (i.e. dont lose gprs connection)
3. Is this problem maybe area dependant? i.e. all devices having problem - are in the same area/ country / city?
4. what is your use case for devices? because devices loosing gprs connection now and then - shouldn't be a problem.
I.e. due to vehicle going to underground parking lot or similar situations.
Unless you want device to stay permanently (or most of the time) connected to server with data link open?
5. are those FMA120 devices you are using single sim / dual sim? if dual sim - are your devices - traveling through country borders? i.e where device would need to switch sim ?
6. or maybe this problem is not about device not having gprs open - but not sending records to server according to your expectations?
Because like i said - not having/losing gprs now and then - in itself is not a big problem usually.