Hugo server not updating theme

After successfully creating a custom theme and updating the site to have that custom theme, I am trying to go back to any of the default themes. However, when I change the theme back to (say) “minimal” in the params.toml file, and then re-execute the hugo server command, the theme is not updated. This is new behavior, and I am not sure what is causing it – I don’t get any warnings when I build the site. I have tried the --disableFastRender keyword, and it does not help. What might be the problem?

Excuse me, params.toml?