I think the way mastodon handles hashtags is the most puzzling of the things I find puzzling as a longtime user. I would expect if I click on a hashtag I'd see all the non-locked content visible to me with that hashtag. But it doesn't include "unlisted" posts. I assume this means the hashtag display is generated via federated timelines, so it only pulls in posts are made available for federation (i.e. listed).