I’m not a linux person so I’m not sure it a permission issue but something is preventing PMS from being able to access those files. I think there is something about users and groups maybe. See if Linux Tips - #22 by ChuckPa helps.
The mobile app might have a lower quality setting when using remote access which triggers the transcode. Locally, it is likely direct playing the file so it doesn’t need to transcode and doesn’t run into the issue. To test, while local, change the playback quality to a lower value. Then while remote, change the remote streaming quality in the Quality settings page to “maximum”. If it’s on cellular, you’ll also want to change the “limit cellular data” to off.
