NodeBB's cache buster is based on its current git hash (so if you've upgraded it will try to send you the new CSS and JS, which works well, but it remains the same if switching themes, which results in your issue)
I suppose the dev team hasn't run into this because we usually run with cache disabled while testing (and because Persona is so awesome so why switch? Kidding)
https://github.com/NodeBB/NodeBB/issues/3573
psychobunny created this issue in NodeBB/NodeBB
closed
Update cache buster when switching themes
#3573
If it works for you, keep it up.
The semi-official way to do this is to fork the plugin you want to use, and make the appropriate changes.
Then, add the original repo as an upstream branch (using lavender as an example):
git remote add upstream https://github.com/NodeBB/nodebb-theme-lavender.git
When you want to update to the latest lavender for your theme, merge or rebase:
git checkout master && git fetch upstream && git merge upstream/master
