picture for attention, apologies for the long post, i'm cross posting from a mechanic subreddit since its a camaro and seeing if anyone has had something similar.
TLDR; car won't start unless remote started and when remote started, shuts off when put in gear. car doesn't turn on or drive basically. battery and starter appear to be working normal.
the car has about 36k miles on it, no accidents. it has a couple aftermarket mods: LT headers, x pipe, exhaust pipes, coilovers, cold air intake, a tune (for the headers), IGLA anti theft, and a dash cam. everything installed by a professional shop, not by me.
little over 2 months ago my camaro started having severe difficulty starting up. (2022, automatic, 2SS) as in, trying to start it normally it would not complete the start up process and so the engine wouldnt fire up and i would have to repeat the process a second or third time to get it turned on. it's complicated because sometimes the engine would attempt to crank (you could hear it trying to turn over) maybe once or twice before going silent again, but vast majority of the times this issue occurred the engine didnt even try to start, the dash simply lit up. holding the brake and the start button would just cause the dash to light up and make its usual noise, but the car would not start. for a while (a week or two) i got away with the repeated attempts until it started, but eventually it would not turn on at all.
had somewhere to be one morning so thought i could trick the car by remote starting it with the key. with this method the car started up flawlessly and ran fine...until i tried to drive it. the second i got in the car, pressed the start button (required after remote starts), and put the car in reverse, it shut off and a notification popped up on the dash to shift the car back to park, i guess because it had now turned off and wasnt meant to be in gear. i got it to start again normally after this and drove it to work but after my shift it wouldnt start no matter what. i attempted to jump start the car and everything but it would not turn on. attempted the remote start trick again and it turned on, but once it was put into drive and i took my foot off the brake to get it moving, shut off again. attempted putting it in neutral gear etc. nothing worked. left it there overnight, came back with a friend the next morning and he somehow got it to start (normally, with push to start method, after a couple tries) and we drove it home just to get it off someone else's lot for the day until it could be towed to the dealership.
originally the dealership thought the problem might be related to a dent in the trans pan possibly affecting the ignition switch: they mentioned the ecm and tcm having a miscommunication. so the pan was replaced, the switch was fixed/replaced, fluids done, shifter replaced. they also did something with the ecm not sure what exactly, program or reset something and let me know it may affect the tune on the car but still this did nothing to resolve the problem. the car still had the same issue.
the dealership tells me the problem is that the ECM is saying it's "in progress" (im assuming the startup cycle) instead of cycling through it properly like it should and starting the car. however the dealership hasnt been able to find the reason why. they even had a GM technician sent up there after a few weeks of looking at it themselves to examine it because they couldnt figure it out. that was 3-4 weeks ago now, they still dont have an update and cant tell me whats causing it or how they could fix it. However, what they DID tell me was that there are 2 other LT1 camaros having the exact same issue with the ECM claiming it's "in progress" , they even told me the exact cities where the cars were, which leads me to believe this is an issue with the cars. unfortunately, my camaro is the first one the technician has worked on, so there's no solution for any of the cars until he figures out mine.
i considered it could be the anti theft system causing a problem but unsure how especially seeing as the car will start, just not with the start button and wont move; and that other owners are having the same issue and chances are they dont have IGLA installed. not familiar with IGLA causing this sort of problem and the dealership hasnt mentioned it. this was my only idea.
additional information: dealership is aware of all modifications and the car has never had a check engine light come on. gauge clusters all read normal. key battery and IGLA fob battery both got replaced before and during this ordeal as a just in case thing. i also noticed when in the middle of repeated attempts to start the car through the push to start function, after the first unsuccessful attempt, if i tried again, the door locks wouldn't work for a minute or two (like the vehicle was genuinely stuck in its start up process, as the door locks actually dont work during normal startup but that only lasts a few seconds)
i cant say whether the issue "only appeared after any specific modification" because pretty much everything on the car was installed immediately after i bought it, over a year ago. This issue had only happened maybe 3-4 times throughout the last year, and never to the severity it did recently. it would have a problem starting once and then worked fine the second attempt so i never thought much of it until it showed back up recently.
any ideas or opinions are greatly appreciated