When using a defaut firework in multiplayer, it will disconnect you from the server with the message: "End of stream".
The firework that disconnects you is a regular firework without no added effects. (Simply gunpowder and paper). But the modified fireworks is just fine.
This can be a big problem because it can completly block you out from the server. If you launch it from a dispenser, its even easier to lock yourself out. If you are lucky, connecting multiple times to the server might get you back on. If not, you will have to delete the player data.
Both the server & client is vanilla. And used default launcher!