M2 Modem issues


We have a number of boards installed in machines, remote monitoring.

We got 3 defective devices shipped back out of 10 in use. They all had defective modem inside. We replaced the modem and they worked out again. They use a regulated power supply of 15V DC in the DC jacket, we also used 12V in the past. We use a Telit modem M2. Any similar experience why the modems are getting destroyed?