macOS Sierra, Plex and iTunes music library

Before updating to Sierra, everything was fine, then I made a fresh install. I have iTunes Match on my Mac, plus some files on my hard disk in the iTunes folder.
I installed PMS and created two libraries: Movies, the works fine, and Music. I activated the iTunes channel, made visible the xml file, linked it to Plex etc, but in the Music library in Plex I see only the few downloaded files and not the whole iTunes Match library. This didn't happened before updating to Sierra, when Plex was able to upload the whole iTunes Match library. I don't know how to solve the problem.
Thanks