Hi Fabio,
Is this issue limited to a specific page or post or is it site wide? One thing I can think of that may have caused this is the preferred editor being switched back to the standard WordPress editor. You can try following the steps in this guide to switch the Post and Page Builder editor back on.
If this is not the problem please inspect your browsers JavaScript console for errors using Chrome dev tools. If any error messages are present copy/paste them into the forum here so that we can inspect them. Hopefully it reveals something useful about your error.
Thank you Fabio! I really hope this helps.