+ AA6YQ comments below
I had also that happen, 5/6 times in the last months. I use AVG , not Defender.
Easy repair from Workspace.
The page, coming after you introduced your call, has all the spots you had when closing last time and no sources.
+ On startup, SpotCollector attempts to read the "Operator Callsign" setting from the Windows Registry. If this setting is empty, then SpotCollector prompts you to specify your callsign.
+ The only way that SpotCollector can clear the "Operator Callsign" setting in the Registry is if you clear the "Operator Callsign" box on the Configuration window's General tab, and then terminate SpotCollector.
+ Thus I suspect that something on your system is making changes to SpotCollector's settings stored in the Windows Registry.
73,
Dave, AA6YQ