Many thanks to all the controllers for an interesting evening.
Air Littoral 123 and Frank both got within 10nm of a place called Bad Ragaz when their world crumbled. They were approaching from opposite directions and I was just about to issue a traffic alert when both stopped. Poor LIT123 tried to reconnect about four times but instantly crashed again and I forget how many times Frank tried.
I'm not sure why I suspected a black hole - maybe it was something Frank said - but I told LIT123 to slew 20nm south and try again. Frank moved to Zurich. When both reconnected they were able to carry on with no problem.
The odd thing is that Alastair went right through the area later with no problem. The only additional scenery Frank had installed was FSGlobal (?) but I didn't find out what LIT123 was running.
The only spoiler during the evening was an oddity somewhere between Innsbruck and Sion that caused FS to crash for two pilots. Later traffic was rerouted to avoid this black hole
I found one of those in the French Alps earlier in the year. Fly over this particular spot and FS always crashes to a black screen.