Hi!
I have been running a 1.20.1 server for a while and I keep seeing the same error every time FTB Backups 2 tries to make a backup it fails to generate a preview.

The error says that index is out of bounds but I feel like I am failing to understand what index it would be trying to get. Every time it is going for index 4 from an object where the length is 0.

I have the logs of the error here: https://pastebin.com/tu4QFaEr
Here are the mods I use: mods

There is a second issue where the NBTQuickSearch doesn't like what it calls "extended chunk data format" and doing some looking around I don't find a way to alter the way the chuck data is stored. I understand that the way chunk data was stored got updated in 1.18 but playing StoneBlock 3 this issue does not show up. So I assume this is another mod doing it and if anyone knows a mod that cause this issue I would love to know which. Thanks!

It appears your Pastebin link has expired.
Would you mind reposting if you still have the log?

Apologies for not getting to this sooner.

Sorry for not replying, have not been signed in to GitHub due to PC migration.
Here is a new pastebin that has the error in it, I have obscured username and UUID in the paste for the privacy of the players on the server. The rest is untouched. https://pastebin.com/D4pdsDhB

The "extended chunk data format" warnings are simply due to the preview generator not yet supporting parts of the latest world data format, but that should not cause any serious issues.

As for the actual error, This appears to be caused by a chunk somewhere having a size of zero bytes,
Based on my understanding of the chunk format, this should not be possible, as the first 4 bytes should always contain data about the size on disk, and the compression type.
So its possible this is a random corrupt chunk, Or maybe minecraft changed something.
Either way, I will need to account for this in a future version. But this error should not cause any issues other than not generating a world preview.

fixed in 1.0.29