bootcamp error

Hi all,

Since this week bootcamp doesnt function as should. In Mac OS all is fine, but when in Windows and trying to Bootcamp back to OSX it says"cannot find boot volume". See pics. There are no updates available, no Windows and no MacOS

This suddenly happened last week. Afterwards i reinstalled Windows (by using Bootcamp) but no fix. Fresh reinstalling High Sierra AND Windows didnt help either. Sure i can workaround this but its not as it should be.

What goes wrong here? Anyone has the fix? Plz tell, thx!