Roon queries your Tidal account for the highest-quality format you are allowed to stream, and then requests streams in that format. Sometimes, Tidal delivers a lower quality stream than what we requested.
We’ve run into this, too, and have reported it to Tidal. I’m not sure whether this is a licensing issue for them, or if they just lack the source material–if we learn more, we’ll be sure to share whatever we can.