RAID 5 two out of sync can't rebuild

Hi Softraid Support,

We have raid 5 setup in our macpro using 4 3Tb hard drives. We used the raid volume perfectly for a couple of months, And then softraid predicted failures in 3 out of the 4 disk we attempted to replace and rebuild one disk at a time.

Disk replacement phases:
- Phase 1: Disk 1 replaced with new Disk -> rebuild successful -> raid volume mounts
- Phase 2: Disk 3 replaced with new Disk -> rebuild successful -> raid volume mounts
- Phase 3: Disk 4 replaced with new Disk -> rebuild not successful -> raid volume in degraded mode and does not mount

We tried to bring in the older Disk 4 back into the system but still the raid volume fails to mount.

We ended up Disk 2 and Disk 4 as out of sync.

We tried to rebuild the raid volume but it fails to initiate.

Please see the attached screenshot and advise how can we proceed.

Thanks