2 reasons i can think of.
1- fuel which was mentioned, this will throw a cel. Im pretty sure you would know if that happened.
2- tire pressures... this is a long shot. But if you reset tpms sitting in the paddock, you can be on track in sport +, than when it sees pressures are under 29, it will throw you into comfort mode until they warm up. Than you have to reselect sport+ or dsc off again.
3- You sure you took it out of comfort?
