Raid Volume Degrading

Hi, I have a problem with Raid Degrading. It all started with power loss, then red diode on the front panel and bad drive (S.M.A.R.T. Data looks almost like new drive, nowhere near threshold values, all the test no problem, just after full drive test it turns diode to red, and tells me to contact WD support)
So, I changed bad drive to new one. And here it started. First I habe auto rebuild option on, so after reboot, it started REBUILDING VOLUME 1 drive 1. After long 12 hours (6TB 60% full) Raid Volume 1 is Degraded.
I reboot the system, same thing
I checked drives, all good, run tests on them all good, all the test came out good except RAID status DEGRADING.
So after while (I also changed second disk) I found out, that even that is says VOLUME is REBUILDING, it does NOT. When I switched auto rebuild off, there is no manual rebuild button, with auto rebuild off, it rebuilds after reboot, and again 10 or more hours, same result.

Can anyone tell me, what am I doing wrong ?

Seems like a one disk is BAD -
read the TOTAL SMART data and run
WD Data Lifeguard Diagnostic - the LONG test from a PC
( you many not get total SMART data via a USB interface connection - )

back up disks before running a diag.

We can’t do low level disk formatting any more so re-formatting my not fix bad sectors-- bad block pool

sell as a 3 disk set - it still will do several raid types