Do you have measures in place to avoid people with high ping, ruining the game for others?
A bad Internet connection will only effect the client with the high latency. The server never waits for a client, so if you have fluctuating ping times you might be in a situation where your inputs arrives at the server to late for it to take it into account. The client attempts to set the push latency based on the ping times from the last few seconds. This push latency controls how far ahead of the server’s time the client is.
So if you have 200ms latency your client will advance the game-states it receives from the server by 200ms and integrate the result into your local game-world. This way your local input will have 200 ms to get to the server, and if the push latency is estimated correctly it will arrive at the server just before the server needs it to update the game state.