Crash while add folder to existing image

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1. OS is the Ubuntu 20.04 with all updates installed.
2. I can reproduce the following crash reliably, i.e. it doesn't feel like a race.
3. It seems the destination image is not changing during the processing or crashing (maybe crash occured in some preparation steps). "Seems" - because i've only checked once, so no guarantees.
4. The destination image is valid and it can be mounted just fine. All content is looking correct.
5. The destination image was produced iteratively, through a series of adding folders. But it gets stuck after some time on a random folder. I reproduced it a few times from scratch. But the process is very time consuming, It takes about a week on 72 CPUs.
6. The destination image is huge (~50GB), the source folders are as well (~10GB each). They all have small differences between them.

I've got quite a few crash reports. Here is the latest two: crash_info.zip