ok, this bug is linked to another bug: getting locked in text selection.
If I am locked in text selection in the main client, I cannot get the contextual menu.
I did find a workaround: I do a fake copy/paste from my keyboard and that makes me free of the text selection lock and brings back the contextual menu
Only the special keyboard keys work, namely ctrl-c followed by ctrl-v does not work.
Nothing extracted yet.
Very often, the user contextual menu is not displayed when I click on the arrow right after a user name (or my user name at the top) or when I right button click on a user.