Invisible signs

After typing a message in a sign and exiting, the text was visible on the sign, but quickly vanished and did not reappear. I tried retyping it, same thing happened. I typed something different and it did not happen, what I discovered was that it seemed to be happening at random because I eventually got the message to appear but my next one experienced the same issue. While typing, I noticed that the text would appear each time I entered or deleted a character, but would vanish in a second. When this happened it indicated that the text would not be visible once I exited the sign. During the same time I witnessed the word "Or" get converted into "##" while I was still typing my sign. I created a new sign and this did not occur again.