I solved the problem of albums being listed twice due to unwanted entry in the storage setting. That’s fine so far. But while I puzzled about the double entries I saw that two identical (mirrored) albums showed different dynamic ranges:
The issue of that album appearing twice and with different dynamic range has been resolved in the meantime. In any case, the albums were exactly the same (must be because I only have one purchased version).
A possible explanation could be that Roon somehow divided the album in two (as it sometimes happens with new material), which would explain different dynamic range values. But then the album being played should have a range value between the two others (11, 15) and not 8 as it did
I can confirm that presently the album shows a dynamic range value of 11.