Shared folder permission problems?

Hi, running OMV4.x on both an Odroid-HC2 as a primary NAS device and on an OrangePi PC as a backup NAS device.

On the Odroid I've been running into problems with shared folder permissions for several plugins, most notably Transmission and Minidlna. Both plugins seem to have stopped working spontaneously, related to access problems for the underlyiong service running them. For the Transmission problems, I've already created a seperate thread, but no solution yet: Transmission - Access denied

Now that Minidlna has also stoppped working with a permissions error, I suspect something might be wrong with folder permissions. That's the main reason for posting this question here; (lack of) access permissions to shared folders seems to be the root cause to both problems, but I can't really figure out why or how.

The OrangePi as a secondary device syncs it's shared folders / file contents from the Odroid, via Syncthing. This includes the /Music folder I've setup for Minidlna to index music files stored there. On my Odroid; Minidlna upon startup generates an error, hinting on shared folder permission issues, see attached file. On the OrangePi, I've setup Minidlna in the exact same way (using the Web GUI) and I don't get the same error. The Odroid has been running the exact same setup without problems for a couple of months, up until recently.

On the Odroid, folder permissions look like this:

drwxrwsr-x+  5 root users  4096 Aug 12 16:55 Music

On the OrangePi, Permissions look like this:

drwxrwsr-x 6 root users 4096 Sep 23 05:46 Music

I've also attached Web GUI screenshot of both folders, see attached files. In the troubleshooting process, I've even grated the Minidlna user and user group explicited RW access to the shared folder and subfolders on the Odroid.I've completely removed the Minidlna plugin from the Odroid, rebooted, reinstalled and reconfigured it on the same / Music shared folder, but then I run into the same error. Selecting a alternative, newly created shared folder generates the same error. On the OrangePi, it works without problems.

I'm pretty sure I'm overlooking something permissions related, as most of my experience is on Windows, not Linux. But because of the similarity between the Transmission and Minidlna problems (both permissions related) I'm kind of worried something is wrong on a more fundamental level in my Odroid setup (corruption?).

Anybody has any clue?