Sometimes the server will cut of text at the end of a sign if you have written a lot. It won't show up on the clients screen right away but other players or restating will see/show the sign is missing characters.
I couldn't find any reports of this which surprised me because I even saw this on Mojang's Christmas live stream.
Notice in the screenshot the 2 and 3 are missing at the end of the first line
Also tying an emoji in a sign will crash minecraft. (Not asking for emoji support, just maybe make it not crash.)