Specifically, the ring states that "solid Objects within that radius appear transparent and don't prevent light from passing through them". Does it apply to solid objects created through illusion?
It seems unlikely that the ring works selectively, and illusions can't plausibly "know" they are being viewed in that way.
By extension, the Ring of X-Ray Vision seems to allow its wearer to inspect the internal organs of a person (be it through selective sight if we consider it to work like Superman's X-Ray Vision, or by standing 30 ft from the intended target so that the target's body is only partially within the ring's radius (RAW explanation). If that's the case, do spells like Disguise Self also disguise the internal organs of an affected character in such a way as to fool a person with a Ring of X-Ray Vision?
For example, would the user of Ring of X-Ray Vision be able to tell if a target has a second heart, or has only one lung, or is undead (dead organs) if that target is affected by spells like Disguise Self?
Moreover, would a Ring of X-Ray Vision allow its user to see selectively through clothes? If so, what about illusory clothes and other illusory objects? I am thinking that it should, otherwise its wearer could use it to automatically detect any illusion, which is not what it says in the description (no truesight, just see through solid objects).