Essel, per my previous post per possible failure of the DI, Backpacker has done an excellent explanation.
You may have had prior failure (or simultaneous) failure of the DI and not known it (normally no red flags on these instruments). In failure mode the DI card would simply not turn or it could displace say 90 degrees and then fail to turn any more (I've had such a failure).
You should consider if your navigation was unknowningly degraded by such a failure.
Anyway a safe return to the ground. (I note you did not have operational GPS, personally I wouldn't start rebooting it in the air - too distracting).
flyme