Custom theme only updates if I run bin/magento setup:upgrade

Newbie so apologies if I get some of the terminology wrong.

I’ve recently started working with Magento using Mark Shust’s docker version and getting along ok. However, my custom theme that inherits from blank has stopped updating automatically.

Clearing the caches either by command or emptying the relevant cache folders doesn’t seem to work – the only thing that seems to update the site is bin/magento setup:upgrade.

Any idea what I’m doing wrong / maybe upset?

Thanks