Not sure what exactly is causing this but when I browse to !formula1@lemmy.world on feddit.uk there's two pinned posts from a while ago, but they can't be seen when visited from lemmy.world
https://feddit.uk/c/formula1@lemmy.world
https://lemmy.world/c/formula1
I'm not 100% on how things work, but I think the pinning can be done at community (local) level as well as on the lemmy.world instance. I think. It worked, that's the main thing!