Hierarchal Fields Not Working - Help Please!

Hello, I have an issue with hierarchal fields.

I've set them up like Genre1, Genre1.Sub1, Genre1.Sub2, etc. and ticked the field under Preferences > Look & Feel > Hierarchy and searching, but it won't work. The tag browser treats Genre1 and Genre1.Sub1 as completely unrelated tags and doesn't nest anything.

I.e.:
Genre1
Genre1.Sub1
Genre1.Sub2

instead of:
Genre1
->Sub1
->Sub2

I've tested it with a brand new custom field, which also didn't work, and found a 2yo post on Reddit with the same issue, but it resolved itself when they reinstalled, which hasn't worked for me.

I've been using Calibre for years and have a lot of customisation so I don't want to start again, but I've got to the point where I need hierarchal fields.

Does anyone have any ideas?
:help: