Fully exit Opus, then restart it again. Does the tree show the correct drives?
If so then the problem could be that the drives do not supply the correct names if Opus starts too early during boot, and do not report that their names have changed when they do become ready, so the tree is caching the drives as unnamed.
I doubt the size of them has anything to do with it directly. Maybe it means they take longer to become ready or there's a bug in the enclosure with how it handles larger drives, but Opus itself does not care at all how large the drives are, especially when just asking the operating system for their names. And Opus is able to get their names sometimes, so the problem must be with the hardware/drivers supplying the wrong names sometimes when Opus asks for them.