Hi Jon,
Thanks for posting! Generally this problem stems from a bug in Visual Studio that corrupts the adornment layer used by NCrunch to display coverage markers. The bug can be triggered by VS package install/reinstall/uninstall actions, NCrunch upgrades, etc.
Forcing Visual Studio to properly refresh its adornment layers is a fiddly process that sometimes requires a bit of messing around. Unfortunately the problem is still rare enough that the resolution hasn't been worked out to an exact science. Usually
uninstalling and reinstalling NCrunch will solve the problem, although occasionally you will also need to reboot or reinstall NCrunch multiple times.
You can find more information
on this thread.
If none of the above solves the issue for you, please do send through a bug report straight after loading up NCrunch on a minimal solution - I'll then inspect the logs to try and identify the cause of the missing markers.
Cheers,
Remco