Limp mode after 70 to 80 mph

I’m having a bit of trouble with my car however nobody can seem to diagnose the problem. I got the car three months ago and within the first month driving on the motorway I reached about 80 mph and the car engine management light flashed and disappeared. I was a bit worried but slowed down and it was fine until the next month I hit around 80 to 90 mph and the car went into limp mode I pulled over and the car was shaking. I turned off the engine left it for a couple of mins and started driving fine again. I took the car back to the dealer and they said it was showing one of the cylinders but didn’t know what it was, told me to test it again so I did, it happened again I took it back and they took it to a garage, again they couldn’t diagnose the problem said it could be some engine coil but wasn’t sure. I left it a week while I was on holiday and took it to another garage, and they can’t diagnose the problem, they’ve tried driving it at that speed and it hasn’t happened again. Any ideas what this issue is/could’ve been?