When firmware 3.10 was released I noticed the problem with IMU communication. It seems it was caused by a protocol problem. When the Phantom was hot it would not communicate the way it should with the other modules. Now the firmware 3.12 have the same problem, but now the phantom needs to be hotter. I already reported it to DJI, like I did when the 3.10 firmware was released. So my advice is: Do not update. Maybe they will allow the downgrade again, but meanwhile, you can downgrade to firmware version 3.08 using the Assistant v3.6.