It sounds like a problem introduced with fixing the advanced strategy behaviour announced here:
https://igpmanager.com/forum-thread/18059
There was an update today which hopefully addresses this:
Darren
Update:
After some reports last night it was noted that when the track had dried the sim thought the track was still wet. Also there was some reports about the car pitting for tyres it had already pitted for.
I believe I have fixed both these instances and will have the new code deployed for 1pm GMT races.