Getting Blank Signs on minecraft multiplayer.

What I expected to happen was...:
There should be text on the signs if there were on other signs some blocks farther away.

What actually happened was...:
The signs were blank (without any text).

Steps to Reproduce:
1. There is not really a way to get it, I tried different things to trigger it again , but it won't reproduce ... It's randomly. Maybe something with the server files. It's a fully vanilla server. It's really strange ... I am really sorry, that I don't know how the bug is happening.