I don’t know if it’s directly related to this issue, but be aware the drive letters (e.g. /dev/sda, /dev/sdb, /dev/sdac, etc.) are mutable and liable to change between reboots of the server on TrueNAS.
It’s advisable to keep a record of which HDDs/SSDs are in which drive bays, using their serial nubmers, for identifying the failed drives in situations like this.
I’d also suggest checking out the excellent “Multi-Report” which, in addition to scheduling regular drive testing, has a neat new future to visualise the physical location of disks in your system.