Are you hammering it out of the box? I tend to join late (last 30 seconds) and physically are never up the front. I just make sure I am pushing out bloody big numbers at the start (really power up with 5-10 seconds to go) and usually get up the front somewhere. If I dont and just go at say FTP, I’m behind the pack always.
I had a similar experience but different other night - in a group ride and re were bunched together nicely during the ride, then part way through they had a sprint - was all of a few seconds - I didnt participate. Ride leader eased off to 2 w/kg. Me and a bunch of others were sitting on 3.5 - 4.0 w/kg for about 1.5 minutes and still couldnt catch the ride leader so I may as well have done the sprint, spent a bit more energy for far less time.
Getting dropped is hard - have you done any races @Simon_Mitchell1 as they are similar - once you are dropped, really hard to get back.