Hello,
It's been a few times since I opened my game and my S2 license has been revoked from the game. Usually it happens if I play another LFS version (in a subfolder of C:/LFS in my case) or when I open a .mpr file (which usually complains it cannot load the S2 track).
It just locked itself (and I'm out of activations unfortunately) and all I did was watching a multiplayer replay within the game a few days ago.
This behavior did not occur in previous versions of LFS. I did not reinstall the game to see if it would fix the issue.
I can't give you much more information since I cannot activate it repeatedly and try to find a pattern.
Hope it'll help others that have the same problem!

Is the LFS directory set as read-only?

I litteraly forgot about this but yes I asked for the devs and got extra licenses, thought the behavior did not occur again.
Some of the files were read-only. I removed that attribute and I also separated both LFS installations. This should be solved.

EDIT: actually I just had LFS deactivated again. Not sure what's going on but I think the next update will fix that.