Quick tip:
If you are using c# in vs code and for some reason the c# language server omnisharp crashes (e.g. you are running/debugging test-cases (in my case xunit)) fastest way to get going again (also with Test to be triggered from within the editor, just restarting omnisharp won't be enough for this):

ctrl+shift+p => Developer: Reload Window

Ref: Found this quicktip in an omnisharp-issue-thread