I kept having annoying glitches here in my own self-hosted WordPress network so I thought to uninstall the package from the distribution (Debian), installing the pure package from wordpress.org itself.
At first I was having the impression of pure bliss.
At first. In fact the more plugins I activated on my network the worse it become.
Customizer Won’t Load
You may suddenly begin having issues with your customizer loading on all or some pages, where the left-hand sidebar loads with only some or all tabs, but the preview never loads. This is almost always due to a conflicting script or widget configured to load on the page you are trying to customize.To solve it, go to Appearance > Widgets and review your widget panels for the widgets you know display on the page with the problem (not including builder widgets). Drag them into the lower-left “Inactive Sidebar Widgets” zone to temporarily deactivate them, then try your customizer again. If this solved it, the problem widget is likely any widget that asks for an API key or needs to connect to a 3rd party, including many Newsletter, Twitter or Facebook widgets. You may safely put the widgets back after finishing your business in the customizer.If this doesn’t solve it, troubleshoot plugin conflicts.
Ok. Ceceppa multilingua conflicts.
Now I’ve discovered that the cache of the web browser were to be blamed for this issue. I’m going to re-enable one-by-one all those nice plugins.