you would have to dig in on a per-relay basis to answer that question, since every relay is effectively its own server/database.

here are some scenarios that could be at play:

- your missing note(s) may still be in the relay database, but maybe the relay isnt returning it because it’s very old. this would probably be a bug in the relay

- the relay is very slow and hasn’t returned your note yet

- your missing note(s) have been deleted or otherwise lost by the relay