majell1n

After upgrading today to 21w17a what I have found is that there are no issues (related to stuttering or invalid biome id’s in the log) as long as it is a newly created world. If I save and exit, then reload the world, it now won’t even open, crashing Java and showing a repeating invalid biome id -1. I can recreate the world and there will be no problems until I save and exit.

I can confirm most of the comments here, especially the well-documented comment from Luna on 4/22.  I began to notice this issue when adding the caves & cliffs preview data pack to 21w16. What really struck me as strange is that broad areas do not exhibit this behavior, such as near the spawn point but even other areas away from it, with no identifiable rhyme or reason.  Then other areas were horrible, lagging while walking between each chunk.  Areas with an issue were 100% consistent in causing the lag, across restarts of the game as well. Further complicating the troubleshooting is that, as mentioned by Luna, it is directional.  It only happens when moving one way into a chunk (though the direction changes depending on the chunk).  You can walk back into the previous chunk without an issue and walk back only to "freeze" for a moment, each time without fail.  When attacking a mob across a chunk exhibiting this behavior the lag ends in the mob being able to attack you without you knowing it.

I can also confirm the "100,000+" error messages in the log regarding "Invalid biome id: -1" and the accompanying message related to many error messages in the log causing performance issues.  These errors occasionally cause the program to hang when loading the world and require a force close.  I am not sure if they are related to the chunk crossing problem or not.

Want to add that normally I work out of my realm but due to issues today with the realm I downloaded my world and played offline (Windows 10) and this issue disappeared with all of my tools with mending. For me, it appears, it is only occurring in Realms.

Confirmed occurs on Xbox One, Windows 10, and Android platforms. Version 1.2.13. Enchanted tools with mending (tested diamond pickaxe with efficiency V, unbreaking III, and mending as well as fishing rod with luck of the sea III, lure III and mending) and it occurs when the XP is actively mending the tool. Sometimes it resolves itself and sometimes you need to switch tools. Sometimes it affects the usage of the tool and other times it does not. For me it occurs without a beacon.

Confirm here too. Latest version - 1.2.13 on both Xbox One and Windows 10 (there is a duplicate bug report MCPE-32550 related to Win10).

It appears mending is still working, though possibly at a reduced rate. I can tell it's working--eventually--on a fishing rod, but not on a pickaxe.