First issue is enable Full Disk Access on Avanpost.

(System Preferences/Security/Privacy/Full Disk Access and drop the SoftRAID into that pane. (on right)

then SoftRAID app can correctly see the disks.

And I think you need to set sleep to "never" to avoid this issue.

I have tried the same enclosure on a MacBook Pro 2019 with Mojave. It seems it does not hang, so problem might be with big sur or macpro2013 + th2 adapter.

The file named Aavanpost is from the bigger macpro2013, and the one named Mojave is from the MacBook Pro. 

The thunderbay is Thunder B, the mac name is SurMac. 

I have removed manually the drive sometimes as i thought that would unhang the whole mac. 

I also see in the console something referring to sleep, but all such energy saver options are off, except screen lock after 10 minutes. The option to put hard drives to sleep when possible is checked off. 

Also, this behavior does happen before the mac enters screenlock. 

Thank you!

P.S. I try to attach the file but it seems it is not appearing in the reply post?

I am having consistent issues with an chassis with 8 drives in raid5 that hangs during copy operations. 

All is good until it decides to hang. There are no ejects, all kexts load fine.

I have even upgraded to 6.2.1, and the same issue. 

I have formatted the enclosure a number of times, and nothing seems to work. After some time, the copy does not work anymore. 

It doesnt matter what i copy, it just hangs. 

Thunderbays 8tb ssds work fine, its just the flexes...

Using a macpro2013 with big sur. 

Have you ever seen such behaviour?

Thank you!