It's not uncommon at all. Your other drives are most likely to fail during a rebuild due to the added stress of continual access during this process.
That's what makes something like RAID 5 on spinning rust so scary.
If all of the drives in the array are of similar age and from the same batch, I'd plan on swapping them all within the next while as each successive rebuild takes its toll on the remaining drives.
Agreed - and double check those backups.
I have doubled and tripled checked. Did a couple restores today with single files and also entire VM's. (Currently using Veeam)