Thumbnails images missing

Ah!! We do progress!! Thanks!
In the Universal content module, I modified the parameter in the tab:
Gestion du contenu via paramètres 
Under the section:
Image
I was on :
Yes, resize
with size parameters

I changed it ot:
Medium size thumbnail

And it now works!

So I guess something somewhere was not liking the parameters like:
https:/&w=110&h=110&aoe=1&q=95&zc=1&f=jpg

I still have a problem with the image of the category displayed at the top of this carousel, you can have a look at the bottom of this page for example :

www.rouchenergies.fr/photovoltaique/en-autoconsommation.html

As you can see, the image of the category is not displaying ont the front-end, although it displays perfectly on the back-end : 
 

For a category, where can I find the parameter to change the way this thumbnail is resized? Can't see it.

PS: I noticed that the icons for Save etc are missing when I'm working on a Flexicontent module (only on Flexicontent module. I don't have this problem with items or with modules not from Flexicontent) 

Any idea about this?