hi folks new to the forum and saw this while browsing and i am 99% sure exactly what the issue is.
i watched the vid and read all the comments and it is almost the exact same issue i had with my old corsa SRI... bear with me.
engine would sound rough as hell when starting usually, at roundabouts and junctions almost total loss of power for several seconds usually, i had the issue for many many months went through all the nonsense of diagnostic checks, replacing plugs, replacing EGR valve, even went as far as booking it into bosch injection specialists for them to troubleshoot costs were getting stupid as they wanted paid by the hour.... eventually pulled it out after the second day almost giving up.
ended up talking to some young kid at the vauxhall dealership he suggested the problem was sticky valves came back with a can of stuff that went through the airbox while revving the hell out of the car lots of thick white smoke...... best tenner i ever spent, never had any issues after that.
just a thought to try before you go mad throwing money at it... Sticky valves was the problem all along.