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)
Link Preview Image Update cache buster when switching themes · Issue #3573 · NodeBB/NodeBBRight now cache buster is based on git hash, which works fine when upgrading. Not as good when switching themes or installing plugins. I suggest modifying cache buster algo to just generate a new one every time forum restarts or reloads
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