I just upgraded to the latest version of wordpress 5.5 and my theme stopped working.
The categories are no longer automatically selected when I click the button.
https://prnt.sc/u030gj
1
This is Trac ticket 51223:
commonL10n and other JS globals removed without backwards compatibility
In WordPress 5.5, the localized translations under commonL10n were replaced by wp.i18n.__ without deprecation notice or backwards compatibility. Plugins using commonL10n now have JavaScript errors introduced by updating WordPress which can break site functionality.
It was fixed in 5.5.1 by adding a compatibility layer. The best fix is to upgrade to 5.5.1.
commonL10n is still deprecated, however, and will be removed in 5.7.