When I use Minecraft, I generally go on the Hive, as it is the serve I most enjoy. A few months back, I realized that messages I send were not being received by anyone else in the server. I didn't get around to fixing this earlier because I barely ever use chat. The odd thing is, I can still chat on realms and private worlds, the only issue is on the Hive. Also, I don't see any of the messages that I hear you would normally see when you get chat banned on the Hive, so I don't think it's that. I tried some of the methods suggested to fix it such as putting the alphabet in chat, and stopping when one of my friends (who were also in the game) told me they could see the messages. This worked for a bit, but when I switched servers it would become broken again.