I cannot open the Georeferencer in both Qgis 3.0.2 Girona and 3.2.3 Bonn.
The plugin worked fine in both 3.x versions until today. It still work in version 2.18.24.
It doesn't seem to open any windows at all, so I don't think it is an issue of windows being in another screen as in some other case.
I also had a look at solution suggested here: http://gis.stackexchange.com/questions/83334/georeferencer-plugin-will-not-load-in-qgis , but they do not apply to my case since I do not have a "Plugin-GeoReferencer" folder in my registry for versions 3.x.
Reinstalling did not solved the issue for qgis 3.2.3
any ideas of how to fix the problem?
+++ UPDATE +++
Same problem with the just installed 3.4 MAdeira version
Best Answer
Problem Solved:
I have been using 2 different second screens: one at home added as left screen, and one at work as right screen.
When I posted my question yesterday I was using the screen at work (so on the right), but possibly the last time I used the georeferencer I was at home so that the windows could have been open on the left screen.
I didn't think the 2 screens were the problem because when launching the georeferencer, I did not see any new window opened neither in the task bar nor when doing ALT+Tab (i'm on windows10). However, now I realize that that is the normal behavior of Qgis (i.e. it opens a windows that is not seen elsewhere but the screen).
Once at home, I tried again to use the georeferencer on a 3.x version and this time the windows popped up in the second screen (on the left). At that point I moved it on the main screen of my laptop and that was enough to see it today at work.
Clearly not a behavior that one should expect... but solved.
thanks @csk and @Leehan