https://lemmynsfw.com/c/[email protected]
works, but
https://lemmynsfw.com/c/[email protected]
and
https://lemmynsfw.com/c/[email protected]
don’t work.

Interestingly, the opposite is true for lemmy.world:

https://lemmy.world/c/[email protected]
does not work, but
https://lemmy.world/c/[email protected]
and
https://lemmy.world/c/[email protected]
work.

And it’s not a NSFW thing, since both of the following don’t work:
https://lemmynsfw.com/c/[email protected]
https://lemmy.world/c/[email protected]