when you use pick block in 24w33a on a block that is in your inventory (NOT HOTBAR) it causes a connection lost screen to appear. when going back in the world, the block is now in your hotbar, just like nothing happened. screenshot shows the connection lost screen.

no mods or texture packs used

how to replicate:
1. place down a block of choice

2. get the block and put it in your inventory

3. use pick block on the block

4. you get kicked from the singleplayer world

you are supposed to have the block you used pick block on enter your hotbar