Major Lag with server-auth-with-rewind

Extreme lag due to server-auth-with-rewind. Since 1.21.70, the most prevalent issue is block lag, with them disappearing when being placed or reappearing when mined.

As of the two most recent updates, 1.21.80 and 1.21.90 the block lag has only increased in frequency, and new issues have been introduced:

1. When walking into a door with a pressure plate under it, the door does not open immediately and the player appears to rubber band forward. Not a smooth experience.

2. When looking at other players, they appear to teleport all over the place. This does not happen constantly, but spikes. (Related issue: MCPE-222309)

3. Entities experience the same effect. Seeming to freeze for a few seconds and then continue to move, just like players.

Usually these things are symptoms of high CPU usage, but whenever I experience these issues or have members of my server report them to me, I can see that CPU usage is below 50% with RAM usage only being 5GB out of 16GB. So it can’t be anything to do with that.

It is also strange that the intensity of the lag is the same no matter how many people are on. Whether it is 3 or 10.

Before server-auth-with-rewind became the default and only option, these issues were rarely experienced. I received much more reports of lag from my server members, and experienced it myself too, after the most recent updates. Initially I had thought it was due to ping issues, but I believe it is due to the server-auth changes. The rubber-banding is annoying and makes it incredibly difficult to play on BDS, whether alone or with a group.

The exact same issue was found under the MCPE bug tracker (MCPE-194468). I thought to repost here as it is more of a BDS thing. There is more information under that link of people testing different settings.