Mastodon for Android requires the hashtag class on anchor elements to treat them as hashtag links:

The web interface does not (and also covers hashtag links with outer "#"): https://github.com/mastodon/mastodon/blob/67a8d4638c6e6a3ef178258504a6535746608c42/app/javascript/hooks/useLinks.ts#L13-L15

This occasionally causes trouble: snarfed/bridgy-fed#1634 (comment)

It would be good to have parity here. Personally I'd prefer the behaviour of the web version, as I think I saw a post where the link didn't cover the "#".