Just crashed my Quad as all of a sudden the Image in the googles froze, then the screen went black with the message 'Image transmittion stopped'.
Distance was only around 300m, flight time 5 minutes on a cold day, so surely no overheat. Firmware on googles, air unit and controller was v01.00.02.00, from mid december.

Transmission recovered after a few seconds, but by that time the Quad had crashed in a field. As it is quite small I couldnt find it anymore.

Any suggestions on what happened??

Any chance you have a loose or damaged antenna? Did you double check your FC amp draw limits on the pad you use to power the Air Unit?

I've had vtx cut out twice now. I chalk both up to having an improvised setup in a frame that wasn't big enough and having weird twisted / bent antenna positions.

I've had about 100 flights since switching to a frame that was designed to carry the Air Unit and I've had 0 dropouts like this since the change. I also ziptie around the Air Unit to hold the mmcx connectors in place (the stock 90deg ones)

The quad was a DC3 BNF from iFlight-rc.com, right out of the box, without any adjustments.  A nice quality build made for the DJI air unit. Didn't have any crashes before, so I don't think there was an issue with the antenna...

There are theories that this type of outage is caused by SD card/DVR recording conflicts in the Air unit causing it to reboot midflight. (Not good!)

Make sure you are using the fastest SD card available, like the Sandisk Extreme.  I actually stopped using my air unit DVR to record, hasn't happened since.  

Yes. I read similar posts as well. But in my case, I only had a SD card in the google, no recording with the air unit.
But strange is also the fact hat the recording for this flight stopped a second after i armed the quad.