As you've probably gathered, none of the development team play AMS so testing gets rather left behind.
There might be something wrong with the way Crew Chief interprets AMS's car class data, or it may simply be that the class mappings Crew Chief has are incomplete or outdated. I suspect the latter. AMS sends a "vehicle name" field, so in order for the app to correctly group cars into a single class, it needs to know what these vehicle names are, and what classes they correspond to. As an example, when you first enter a session the app will log the car names to the console, like this:
Code:
17:53:47.671 : EventIndex: 10
17:53:47.671 : SessionType: Race
17:53:47.671 : SessionPhase: Formation
17:53:47.671 : SessionIteration: 0
17:53:47.671 : HasMandatoryPitStop: False
17:53:47.671 : PitWindowStart: 0
17:53:47.671 : PitWindowEnd: 0
17:53:47.671 : NumCarsAtStartOfSession: 19
17:53:47.671 : SessionNumberOfLaps: 0
17:53:47.671 : SessionRunTime: 3630
17:53:47.671 : SessionStartTime: 04/25/2019 16:53:47
17:53:47.671 : Player is using car class: "Opala86" at position: 5
17:53:47.671 : Multi-Class event:
17:53:47.671 : "Opala86" (unmapped)
17:53:47.671 : "Opala" (unmapped)
In this example the app doesn't know that Opala and Opala86 are the same class, so it treats the race as a multiclass event. It's the same for GT3 or whatever. If you could repeat this process and send me the vehicle names that are in a single class, I can add them to the app's data for the next release.
In the mean time you can force the app to assume all cars are in a single class with the "Force single car class" option in the Properties screen.
The issue with the app grumbling about your start sounds like a bug - it sounds like the app thinks you started in a much better position to your actual start position. Was this a standing start or a rolling start?
[edit]
actually I think i just found and fixed that start position issue - the app is getting inaccurate position data when the lights go green so I'm allowing the app to update the starting position 0.1 seconds after the green light which appears to have fixed it. Will be in the next release