Steps to reproduce the issue

Click save to save changes made to an article

Expected result

Article saved

Actual result

When save button clicked a popup tells me "Error, form cannot be submitted as its missing required data. Please correct marked field and try again".
Category* one of the options must be selected.
However the category selection box has no categories available to choose from (there are categories set up), the only way to move on is to reload the page which takes me back to the previous successful save.

System information (as much as possible)

Localhost
Joomla! 4.0.0-alpha9
PHP 7.2.14

Using JCE editor

Additional comments

Just started to happen today for no apparent reason, I was editing an article by setting up bootstrap responsive grid column sizes for breakpoints