I have had a similar thing happen in the past. I initially though it was a mechanical problem with the TX (a futaba 8FG) and even though they could not replicate the problem in the workshop, the distributer replaced the TX. Later though, I realised that the problem was more likely a slight a programming issue. I think as I was launching, the brake stick would move slightly (either just from the force of the launching or my finger moving it very slightly) and the flaps would deploy a bit, and crucially, the down elevator compensation. This, I believe, caused my crashes.
I now, sensibly, have changed the programming so that the the brake stick does nothing for the first few 'clicks' and the elevator compensation is less severe. I have not had it happen since.
BTW, I was told that the engineers had quite a laugh trying to replicate the conditions of a DLG launch in the workshop!