The LG V20 was released 2016, October, and originally was Android 7, with an upgrade to Android 8 only available in Korea. So has that changed? Are you on Android 7 or 8?
Also, I should have asked, full version of MC (i.e.MC24.0.47?) and are you using the 64 or 32 bit version?
MC24 64 bit was updated to support Handheld sync a little while ago, but it did require some tweaks to work with my Sony Android 8 phone. Maybe the LG works a little differently and also needs some special handling. Testing was only done on HTC, Samsung and Sony devices I think. Maybe also a Nexus. There were instances of media files being saved to the root directory instead of a location based on the rule specified.
Maybe try this; under Handheld Options for an Android device you can now specify various Playlist formats to be saved to the device. I use m3u with relative paths, for example. Set up your Handheld Sync to the LG to use one of those formats, then copy the resulting playlist file to your PC so that you can open it and have a look at the paths saved for the files on your LG. If the paths are correct, then I would expect the Audio Path to work. But if the paths aren't correct, something is probably going wrong at the MC end. That test doesn't give an answer, but it might provide a hint to a JRiver developer, one of whom has probably noticed this thread by now.
Handheld Sync really does need some more love, particularly on Android.