Enabling rewrites for custom taxonomy permalink stops term archives from working

I have a custom post type, cultivar, and an associated custom taxonomy, taxon.

The post type has the base archive at /cultivars, and rewrites enabled so each post is at /cultivar/post-name. This works as expected.

With rewrites disabled for the custom taxonomy, each term archive is at /cultivar/?taxon=term-name. (As an aside, I have a widget installed which lists all terms, and the URLs in the widget incorrectly go to /?taxon=term-name instead. This might be an unrelated issue but I’m mentioning it here in case it’s relevant to the main problem).

With rewrites enabled for the custom taxonomy (rewrite with front: false, and hierarchical: false), each term archive should be at /taxon/term-name. When I go to a term URL, the page title correctly says “Term Archives”, and the breadcrumb at the top reads “Taxa > Term”. But the content just says “Nothing found”, even though there are posts in that term. If I try enabling rewrite with front, so each archive should be at /cultivar/taxon/term-name, the same thing happens at that URL.

What’s going wrong, and how can I fix it? I have various other plugins installed (WooCommerce, Yoast, some other small tweaks) but none that directly deal with my custom post type or taxonomy.

The page I need help with: [log in to see the link]