Lag on multiplayer is horrible at times. The game I play with some friends we have all been playing together for months is now lagging like crazy at times, whereas we never 'saw' the issue with the Switch Edition. Same people, and we have tried with the new imported world and also started a new unlimited world from scratch. It's pretty consistent. While we think we might have narrowed it down to a player's connection or two, but can't be sure without tools and even after that player sitting out for a while a new person will come in and we are back to huge lag problems which then throws it all back into question as to who or what is causing it. That then leads to the issue of bad coding when it comes to lag.
A. Some of the issues we have all noticed is that the game locally plays your moves when lag is occurring and then once the lag resolves it will then replay just a fraction of the moves it allowed you to play. This leads to people being stuck in walls if they were digging, dropping from the sky if they were flying with elytra, and having a whole row of blocks just disappear. The blocks disappearing is annoying if you are trying to build something but deadly if you are doing something like bridging lava. I mean a couple of us are about to rage quit it's so bad at times.
B. Another issue is that you can switch items in your hand and if you are in a lag situation, find that you are now digging with a torch, because the cursor will just roll back to whatever you had selected at the time of lag. This and the other behavior are totally unacceptable when lag is happening. It should not allow you to make a move, or worse let you make a move and then undo it once lag is removed. And letting you change your item then changing it back is terrible. Like I said, rage inducing at times.
C. The host of the world I play on has commented that he thinks some additional lag might be occurring during the autosave. There are no settings we can find to space this out or make any modifications so this is more of just a speculation at this time.