Hi. I had got the same problem. I was able to run pFBA 4.4 through installed HBMenu. Try this. Maybe this will help you. Or try converting pfba.nro to nsp format, install and run it.
I could claw back 14tb by only doing 2 parity disks but I feel like with 13 disks in the RAID I'd be kind of pushing my luck on rebuild time if I encounter a disk failure