I have 2 servers like this. Issue with both is that hotspares fail on patrol reads. I narrowed it down to the fact they go from power transition to unconfigured bad state when patrol read starts. I have "worked around it" by configuring controller not to put hotspares in low power state.
On a side note I have another SERVER CHASSIS P4308XXMHGC with ITL S2400SC2 SERVER MB and RSBL040 that has no problem spinning up hotspares for patrol reads.
All 3 server use the same controller firmware and using the same model/size hard drives and operating systems. My best guess is there may be an issue with the P4308RPLSHDR backplane firmware, but I see no update to it.