Effect of different ripping strategies on Roon's album recognition

I’ve had a number of problems and issues with ripping and loading opera sets. The metadata services are often flaky, and, whatever the ripped metadata says, Roon sometimes takes its own view… and that is sometime associated with particular discs from the set being skipped. Three different strategies produce different results:

  • Ripping to Apple Lossless via iTunes - normally looks fine, and Gracenote seems to be, for this purpose, a better service than others
  • Ripping to FLAC via dbPoweramp behaves differently depending on whether:
    – I rip to my Mac’s drive (often causes problems including poor track titling and skipping files)
    – or to a scratch folder on the NAS where the media sits (which seems to be more reliable, and better from the metadata point of view. In the latter case, Roon is watching other folders, and I transfer the files to one of those when I’ve assembled and sorted titles in the scratch folder)

Anybody else had this sort of experience? And, if so, can anybody shed light on what makes the differences?