In the SMART details for that drive look for "Reallocated sector count", "Reallocation Event Count", "Uncorrectable Sector Count"... The Raw Values should be zero, if not that means there's some bad sectors. It's not always end of the world, if there's only a few. But it may be an indication why Scanner is maybe showing an issue. If those are all zero, then I'm not sure what else to look for.
Does scanner show what that "1 warning" is anywhere? You'd think that it would show you somewhere what that "1 warning" is.
I'm fairly new to Stablebit Scanner myself, but hopefully you can figure this out somehow (and a Stablebit rep stops by too, hopefully). Otherwise I'd put in a ticket with them. I did ask a question to them about DrivePool and they responded within 24 hours.