Someone types and nothing happens. That has a handful of causes ranging from «they are muted» to «your chat plugin is broken», and the order below rules them out with the fewest questions.
Check in this order
- Can anyone see it, including them?
If they see their own message and nobody else does, it is a plugin filtering or channelling it. If they do not see it either, it did not leave their client.
- Are they muted?
By a plugin, or by the vanilla chat toggle in their own settings. The second one produces a player who is convinced the server is broken.
- Did they set chat to «commands only» in their options?
It is a real Minecraft setting, it persists, and it is set by accident more often than you would think.
- Does chat work for everyone else?
One person is a client or a mute. Everybody is a plugin, and the console usually has an error at the moment someone typed.
- Check for two chat plugins
Two plugins both cancelling and re-sending the same message can end with neither version delivered. This is the case where nothing errors and nothing appears.
- Look for a chat filter
Anti-spam and word filters silently drop messages by design. A filter that is too aggressive looks exactly like broken chat, especially to the person being filtered.
If a message is blocked, tell the player it was blocked. A chat filter that swallows messages without explanation makes people think the server is unreliable, and they will not report it — they will just talk less.
About signed chat and warnings
Recent versions sign chat messages so their origin can be verified. Plugins that modify messages interact with that, and depending on your setup players may see a warning icon or a modified indicator. That is a version and plugin question rather than a fault, but it is worth knowing before you go looking for a bug.
One typing, one watching. Thirty seconds of that tells you which half of the pipeline is broken, and everything above becomes a much shorter list.
A message typed by a default-rank player appears for another default-rank player, in the same channel, within a second.