EDIT: Correct --noFastRender to --disableFastRender
What happens if you do:
hugo serve --disableFastRender
If you look at Code in tags/baseof.html and tags/list.html only works after hugo serve when --disableFastRender is flagged that helped someone else with a similar issue.
I have also seen this behavior were using --disableFastRender gets tags page serving correctly (and for me, the issue only affects the server, not building for production).
In my case the suggested
hugo --printPathWarnings
had no warnings, so the issue wasn’t the same as the post I mentioned, but the --disableFastRender did work.