Hey @Saturn94,
Based on the information you’ve provided above, it sounds like you may be experiencing an issue we are currently working on a solution for regarding the playback of AAC files, though this typically effects all AAC file playback. Though we are working on a solution, some have found more immediate success by update FFMPEG, as discussed in this thread.
To confirm whether or not that is the behavior you’re experiencing, I’d like to propose a test. If you have a Windows or Mac device you can temporarily install Roon on and use it as a Core, does it exhibit the same behavior, or is it only with the Core you’re currently using?
Thanks,
Dylan