R9 Stab OTA problems?

I had this crash today and either I have a dodgy FrSky R9 Stab OTA receiver or there is a problem with compatibility with OpenTX 2.3.9?
I flew this Tundra with this R9 Stab OTA running OpenTx 2.3.7 with no problems. Since I updated the firmware the R9 Stab keeps restarting.
Before the crash I flew a Ranger G2 with an FrSky S6R onboard and had no problems.
My Transmitter is a Horus X10 Express.
I then flew Tundra No.1, FrSky R9 Stab OTA and as you can see, it dropped out of the air.
I then flew a second Tundra straight after this crash using the same Transmitter and an S6R and had no problems, had a good 20 minutes flying.
I followed up the flying session by flying a Bonanza with an R9 Slim+ OTA, no problems. Then a ZOHD Dart 250g using R9 Slim+, no problems and finished off session flying ZOHD Dart 636 using R9 Slim+ OTA, again no problems.
On all models except the Tundra 1, I did not have any range issues, no drop outs, nothing, so either I have a dodgy R9 Stab receiver or the R9 and 2.3.9 do not like each other.
(P.s. - I have since rebuilt the Tundra and did a clean install of the R9 Stab and when I went to calibrate the planes servo extremes with the radio, the R9 Stab kept restarting before I could complete the calibration. I then placed a new S6R in the Tundra and it completed all calibrations with no problems?
FrSky are going to investigate I think?
Anyone else had problems with the R9 Stab and 2.3.9?
Thanks.