To reproduce it, open https://meta.discourse.org/new-topic?tags=chat in an Incognito window or logged out: it redirects to /latest, but no login popup is open.
If you remove the tags query param or use a category instead, like https://meta.discourse.org/new-topic?category=support, the login flow is started as expected.
Another (very) minor issue I noticed while testing is that if you use /new-topic?tags=restricted-tag, it still fills the tag field with a tag that can’t be saved, like https://meta.discourse.org/new-topic?tags=official.