Issue with group avatar

When I create a new group, I can’t upload the avatar..

Attached the image of the previosu step (n. 5)

I follow the step to create a new group, and when I come to step n. 6 (in the image, text is “Immagine Copertina”, as my site is in Italian language..) NOTHING is displayed!

I can only see two buttons, back to the previous step or go to the next one (that is: invite users..).
If I click to go to the next step, a blank page come and ask me “Are you sure? Retry..”

So, you can’t complete a new group creation..

Now I disallowed the avatar group, so I can have group (without avatar..), but I want avatar in group..

Any solution?

I’ll give you link to my web site in private, if any moderator reply me.
(please, teach me as set a “private reply” as I don’t want to share my link)

Waiting for a solution.