When I play songs from the (windows 10) desktop player or my android devices (Sony Z5, Samsung Galaxy Tab S2) to my chromecast audio, it works without problems, BUT all my own/local songs, already downloaded on all devices, where ignored and skipped!?

Since days I'm in conversation with the Spotify support but I only get replies nothing to do with my problem.

I use newest app versions on all devices.

I can't find any restrictions regarding this at the Spotify help site. Except the hint that local files are not possible with Spotify connect.