Hi @ACvitus,
Thank you for the report. Low-res cached mages will appear in the Now Playing screen when ARC never actually cached a high-resolution copy of the artwork. This can happen under one known circumstance at this time: if this track was downloaded to the phone, but you hadn’t visited the Artist or Album Details page while online. In these cases, the lower-quality image (from the queue, playlists, etc.) will expand to fill the Now Playing screen. The team is investigating this issue and will report back in the EarlyAccess thread @Suedkiez linked above (here).
The second issue you’ve reported - lockscreen displaying the incorrect artist - is a known issue for which we have a developer ticket. We aim to resolve that swiftly within the next several builds.
We truly appreciate your diligence and precision - thank you for taking the time to type this up and provide screenshots. We’ll provide an update here once the ticket makes motion, and I’ve retitled this thread accordingly.