(Also happens on iOS)
Related to MCPE-1198
When a player handles an unknown item (like 122), all the clients (and possibly the server) crash. This can be done using a modded client.
Linked issues
Comments 4
Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
this happens because the client has no idea what on minecraft the block is and it "panics" and crashes. (Mainly because it's android and rarely happens on an iOS device and ios's client is Mach more suitable In a panic. (Hope this helps 😉