I hadn't time to investigate more. I stopped the server on my Pi.
A friend gave me a Pi 3B+ (my current one is a 3B). I thought about switching the SDcard from the 3B to the 3B+, but then the 3B+ alerts of insufficient power and refuses to boot. With another sdcard, it works fine (I have a retropie one and a blank Raspbian).

Haven't found explanations on the net. I guess it's an incompatibility of some sort with that brand of SDcard...

I'll use the 3B+ to work out an ssb-pub as I find it sensibly faster (check was the launch of LibreOffice ;) )... later