I am not sure, without an engineer to dive into the partition maps, where the source of the problem is, so I am recommending both volumes yes. I don't want you to do A, and still have an issue.

What do you mean both volumes? Only "A 4TB RAID 1" is having issues and other drives/volumes are fine.

Maybe you meant to split the other drive? I have the old drive(HGST) and the newly installed drive(WDC) that makes up "A 4 TB RAID 1" See screenshot below:

Yes, but you will need to deal with both volumes, I think.

The main volume may be part of the issue.

Are you able to "split mirror" on both A and B?

Here is a weekend project...

Split mirror on both volumes.

zero disk on A first.

Initialize disk with SoftRAID, 100 sectors

erase disk with Disk Utility.

Carbon Copy Cloner from A to new volume.

Now you have a Disk Utility volume for both A and B.

Initialize both source disks. Create new SoftRAID volumes on both, A and B

CCC to A and to B.

Convert to Mirror on both.

Let me know if this is understandable.

There is something wrong with the SoftRAID status partitions on one of the volumes. It may be the older one. I cannot interpret the volume status partition, so need to ask an engineer to look.