This happens to me Every time I try and open the chat when I’m a client in a multiplayer lan world. It’s fine when I’m hosting it or in single player.😞
If you have this problem you could try downloading the OLD launcher. It worked for me. Get it at this link:
https://s3.amazonaws.com/Minecraft.Download/launcher/Minecraft.exe
Is there any possible way I could downgrade my launcher until this is fixed?
Fixed with the 1.2.13 update