Here Is The World File:
http://www.mediafire.com/file/cck6hx1v149dvy5/Ultra_Land.zip/file
This Is the Latest Copy Of The World That I Made Today If That Is Okay?
If This Helps, I Do Have A Few Texture Packs On That Were Made For 1.15.2 But Can Be Used In The 1.16 Snapshots Too, But Since Optimizing Your World Converts Everything To The Latest Snapshot Version The Texture Packs Aren't Compatible, But Since I Have Them On Whilst I'm Optimizing The World, It Could Cause A Fault In The Process. Just A Theory!
I Can't Fit The World File In The Email, Where Should I Upload The File?
I Have Checked The Chunks The Log Said It Had An Error With And Nothing Is Wrong With Them!
The Log Is In The Link Below:
https://paste.ubuntu.com/p/FbGnRcvnkp/
Please Get Back To Me If There Is Any Information On How To Resolve This Manually, If I Have To.
I've Seen This Bug Too, The Only Way To Stop It Before This Bug Is Fixed Is To Just Break And Replace The Block The Rain Is Falling Through.
It's Been Like This Since Snapshot 20w16a!
Can report that this is happening in the new 20w22a snapshot too.