Description: My friends and I have been playing on this Minecraft Realm for over a year now, and we have started to experience some significant issues as the world size grows larger. Occasionally and apparently randomly, certain chunks will "roll back" to a previous state, reverting all blocks inside and items within chests to the state previous. Player inventories are not changed, and neither are other chunks in the world. This could potentially open the door to an extremely powerful dupe exploit similar to the "book dupe" seen in Java Edition.

Steps to Reproduce (must be done on a realm!):

Step 1. Obtain a significantly large superflat world in size (will update with exact size of our world)

There is no easy way to do this, but you could potentially increase the world size by /filling large areas, or filling shulker boxes with filled books

Step 2. Download a Chunk Borders Resource Pack (Optional). This is very helpful for the second step

Step 3. Fill a large, flat area (like the one shown below) with a clearly distinguishable block (like red concrete)

Step 4. Leave the realm, then rejoin in 30 seconds (enough for the server to create an auto-backup)

Step 5. Mark each chunk (like below) with a clearly distinguishable block(s)

Step 6. Rejoin the realm (or unload the chunk)

This may take awhile! It does not happen every time, and is in fact quite rare. 

IMPORTANT: Although I have not tested this, it is not impossible that this glitch is voluntarily reproducible using lag machines (or large amounts of written books) in the target chunks. You can try this if you want.