Hi @Uli_Lennartz,
Thank you for your patience.
Reviewing this case, your Roon database is almost certainly too large to sync reliably with ARC.
Diagnostics show your library contains roughly 700,000 tracks. ARC isn’t built for full-scale library management like RoonServer, but it still needs to maintain the object graph for the entire database to track changes while offline. Syncing a library of this size would require transferring metadata, artwork, and track information for hundreds of thousands of objects in real time, which puts enormous strain on memory, network bandwidth, and processing. On top of that, Apple and Google impose limits on how much data any app can request on a phone, which makes this practically impossible.
To use ARC reliably, you’d need to rebuild your Roon database with a much smaller object count. Simply deleting or removing files won’t work, because Roon still retains the objects in its database. You’d need to start fresh and add only a portion of your library. In our testing, libraries of 100,000–200,000 tracks sync reliably on high-end phones.
We understand this is frustrating for users with large collections, but it’s a limitation imposed by the mobile platforms themselves, not by ARC.
Please let us know if we can answer any questions.