I created a test playlist with 5 high-resolution flac files from different artists and albums. I clicked "Upload to Cloud" and it informed me it uploaded it and saved an MPL file on my desktop. The MPL has only one file in it, the last one. When I look at the upload details, the first four say "failed". The MPL will open the one successful file.
I repeated "Upload to cloud", then clicked "Details" and it shows all five files "In Queue". After clicking "Upload", I'm immediately presented with an error dialog, "Errors prevented uploading one or more playlist tracks. Please try again later."
The first four files existed during previous efforts to upload, but the 5th file was an AIF which doesn't seem to be supported. I replace it with a flac in the playlist, and that file seems to be the only one I can play. When I visit my Cloudplay from within MC or a web browser, it does not show that any files or playlists exist. I switched to IE within MC before I tried uploading anything.
MC 25.0.37 64-bit win10