Following version 1.17.30, my long-standing realm world is experiencing corruption. Immediately after the patch, the world file size randomly jumped 700 mb (from about 1gb to 1.7 gb) after a couple hours of play. 

(Note: My players have a world limit, so new exploration did not cause this.  I’ve investigated the file using mcc tool chest, and no new chunks have been explored).

After the file size jump, the world began slowing down until the lag made moving or placing blocks impossible. After several more hours, the realm no longer allowed anyone to log on (stuck on loading world screen). The backup from this time cannot be entered in single player mode, either.

I replaced the world with a backup from before the file size jump, but from after the 1.17.30 update. After another day, the process repeated (the file size jump, the slow down, the inevitable inability to load the world).

My next troubleshooting step is to replace the world with another backup from prior to the update and see if the corruption occurs again. I have not yet done this,  as I do not want to ask my players to keep working on projects that will likely be rolled back.

Some background info:

I’ve run this realm for over three years. We had a very similar problem happen immediately following the December 2019 Buzzy Bees update (1.14). It took me four months to get my world back online for my members; our spawn chunks had become corrupt somehow due to the update, and I had to do hours upon hours of very meticulous work to get our world functioning again. I still was not able to run the world on the realm until a hotfix on April 15th, 2020 (patch version 1.14.60). I’m not sure if somehow a similar bug that was addressed by that hotfix was introduced this time around as well, but the after-effect of this patch is very similar.

Thank you for taking the time to listen and look into this. If I can provide any further information or files, I’m happy to do so.

Editing to add information:

Browsing reddit for others having this issue, and this seems to only be happening to worlds that are uploaded to realms, so this report should potentially be in the realms section instead.