It's not Voyager's fault, Lemmy has always promoted dead and abandoned communties as "trending". The grouping is useless and can always be safely ignored.
Not sure about the top and bottom ones, but I'm pretty sure those @a.gup.pe ones are Mastodon "groups". They're a reflector that you tag into a post to have it shared to its followers across all instances, rather than just your local instance (as with hashtags).
They're a workaround for one of the limitations in Mastodon, but they work. I expect they'd appear empty if viewed in Lemmy.