It's not just you. It's something wonky in the coding but occasionally it does this when you hover over a citation. I don't know what the exact reason is behind it but it's nothing to really worry about. Seanie or Whoreos could give you a more technical reason if they see this thread.

tl;dr KusabaX shitty programming.

I don't know that I've seen that exact message, but it sounds like a timeout error, possibly browser-specific. Sometimes with a weak wifi signal, when I hover over a cite which points to a post in another thread, or one which is not currently loaded because of the 'last 50 posts' feature, my connection will derp and I'll just get a small empty box. I would guess this might be the same type of situation with a different browser or newer version than mine.

Or it could be a case where someone linked to an non-loaded post which was deleted/404'd.