I managed to fix the same issue for me by using the settings in the image attached.

I can confirm 11.3 Beta 3 has RESOLVED the problem of the drives not being able to mount. I can now access my Thunderbay drives. SoftRAID v 6.0.1 b52 ...

Mac Mini M1. 256 & 8gb. 2 Thunderbay 4's and 2 Thunderbay Mini's all Thunderbolt 2 - 11.3 Public Beta 2. - SoftRAID 6.0.1 b52 SoftRAID lau...