Hi Peter, your dev version fixed the problem perfectly.
Thank you.
Final note on this, is there a way to control the order of the group buttons as it doesn't seem to follow any obvious order (not alphabetical or ordering from what I can tell).
Sorry it seemed to have fixed it at first, but now it is only showing one of the group buttons, and the rest has disappeared.
I had gone into Content Templater, and used Filter Options to only see one Category. It turns out it would then only show that category in the Article editor (so that one group button). I went back to Content Templates and removed the filter (that one category) and set it back to -Select a Category- and now all the groups and buttons are showing as they should.
Hi Peter, just to let you know, the issue with the group buttons not displaying in alphabetical order ( that you fixed above in Joomla 4 ) is also present in Joomla 3 (sorry I should have mentioned it earlier).