I ran back and forth to the computer for a while last night, without paying much attention. When I began doing so again, I suddenly became aware that the CPU was running at absolute maximum, the temperature was at 82°C, and the fan was working overtime, and this had already been going on for half an hour or so.
Of course it was Logos, doing I don't know what (nothing I had told it to do, anyway). I shut a tab or two. No difference. I tried to quit. Endless syncing or whatever, with no result. So I had to force quit.
I'm sending the logs by mail. I see a number of errors in them, at many different places, but none of them means anything to me.