If it's not a RAM issue could be corrupt LUKS headers, do you have a backup of those?
In any case two simultaneously disable disks is usually not a disk problem, SMART looks OK for both and they are on a SASLP which is not recommended for Unraid and known to drop disks sometimes, so you might want to check if the actual disks mount with UD and if yes re-sync parity instead.
Also I wouldn't recommend encryption unless you absolutely needed it, it's just another layer of complexity, but if you keep using it make sure you backup the LUKS headers.