My VW Tiguan mk2 - 2017, 2-liter diesel TDI 150 engine and a 7-speed DSG transmission. The car has covered 71k miles.

While driving, the car occasionally jumps out of gear into neutral and then back into gear. Pinpointing when it might happen is challenging, but I've made some observations:
It’s hard to suggest when it might happen - but some observations:
1. It’s worse when the car in cold
2. It’s worse under hard acceleration (or more noticeable as the car revs in neutral)
3. The gear indicator on the dash disappears when going into neutral and ‘ACC disabled’ shows on the dash. It then goes back into gear and everything is normal.

Upon recommendations from various garages, I decided to go for a DSG service. Unfortunately, the fault persisted. Despite a full diagnostic at the garage, no error codes were identified. Initially suspected to be a mechatronics unit problem, it was removed and sent to ECU testing. This morning, ECU testing informed me that no fault has been found.
I am genuinely perplexed about the next steps. Having already spent £800, it feels like I'm back to square one.
Does anyone have advice on what to do next?