You can try check --repair but only after making sure everything important is backed up, if it doesn't work or if it re-occurs best bet is to re-format and restore the data.
You should be able to see SMART info for SAS drives (except some Seagate models on some versions due to a smartmontools bug), but there's currently no SMART attribute or health monitoring for SAS devices.
How to reproduce:
-start with a dual device pool in default raid1 profile
-stop array, assign new device as a replacement, start array
-result:
Unmountable: Too many missing/misplaced devices
It worked on -beta25, it doesn't since -beta30, so it was introduced somewhere in between, diags below.
tower15-diagnostics-20210107-1504.zip
All 3 disks have the same ID, that won't work with Unraid, devices need an unique ID, looks like your using a NetApp enclosure, no experience with those but other users have been using them and they usually don't do that.