Just quit and reopen Minecraft, and it should be fixed.
Fps is heavily dependent on the computer and settings, this should not be a bug associated with Mojang. try to lower your render distance, lower your graphic settings and use optfine.
Yes. If you are running on a 1.14.4 server, it could crash the server
1: It is not Minecraft's responsibility to help you save your game/keep track of it.
2: You said in version 1.12.2 but the Affect versions is 1.14.4
3: You provided no evidence in helping determine the cause
Can confirm that this is occurring again in 1.18.1. client freezes for approximately 1-2 seconds whenever a player is silent for a while and sends a message.