Chated with my friend on a server from Aternos.org and did some pranks using /execute as @r run w. Suddenly I couldn't read some messages my friend sent in chat. The same thing happened to him. All text we sent was turned into weird symbols/squares. I didn't take much screenshots and we will try to repeat this.

In the seven screenshots I attached, you can see my friend (upptyplague9) saying weird squares as I said. On his screen I did the same. A relogin helped after two tries.

We talked in Swedish language.