Yeah, I didn't say anything at all that might be muted and I'm now unable to send chat messages to anyone.
Image of the chat history:
(as far as i know this is when i was blocked from chat, however it may have been earlier and i didn't notice)
At this point only one other player was online (waxrevenge) and as far as they could tell they hadn't blocked me. But when they left the server and i was alone again, it no longer said "The server has blocked your message for some players" after every chat message i sent. However i have not yet tested whether it says this with other players online, or just waxrevenge.
Is anyone else having this issue on a java realm? (I am)