TB, Win10: deleting a single event (open event, press delete) killed all events in display for that calendar (at least over 3 months, didn't check far into the future). There are 4 calndars on display in total (all ics).
Fortunately, I thought to hard kill the TB process by taskmanager. After restarting TB, the events came back (but not the deleted one). So the ics file seems to be ok. But still, why did all events disappear from display? Unselecting then selecting the calendar for display did not help.