Still sounds like a bad RAID controller to me. Having to do pool rebuilds constantly are (in my direct experience) controller problems 100% of the time. If the controller is under warranty I would replace it. That's just my opinion so maybe someone else has something else to offer.
Sounds just like the screenie I posted and both were bad controllers. Replaced them both within a month of each other.
Boss said I was wrong. Solidstate devices don't fail like that within a month of one another he says. Ok....so I replace them both and both servers run flawless.
Boss had me do all this bs, firmware updates, etc. Waste of time, but I had to listen. Then I simply replaced them and everything is perfect.
But still, maybe someone has another idea. If it has been running great and then all of a sudden you started having issues, I'll blame hardware because those errors have never resulted in a software issue - ever. Not for me.