Hopefully the fix to http://www.ventismedia.com/mantis/view.php?id=11132 will resolve this issue as well...

I'm pretty sure that metadata of existing files is only synced if there were changes since last sync. The lack of ratings in MMA may be a problem left over from an old build, but as no changes had been made in MMW to the files no ratings were synced to MMA.

I did a touch-up of the rating for each file in MMW, e.g. changing 5 start => 4 starts => 5 stars, sync, and can see the ratings in MMA after the touchup. I wasn't doing the fresh/full sync before (deleting all the music and re-syncing it) because of the music collection size - approx.35GB, it takes some significant time and unnecessary wearing out the flesh memory. So there is a simple solution to my problem, but why would MMA allow having no ratings in the database while
a) each local mp3 file has the MM_Rating tag, and
b) MMW was syncing the database with MMA, supposedly seeing ratings on the PC side and no ratings in Android?
And somehow the initial ratings were lost, after I did the very first sync with the actual file transfer between PC and the phone.

I can't reproduce either on freshly synced files with MMA 164 and MMW 1658. Ratings are shown for files synced with these 2 builds.

I'm unable to replicate this on various devices--the only problem I do see is that ratings can sometimes fail to update on tracks that already exist on both the server and the device.

I've added this to http://www.ventismedia.com/mantis/view.php?id=11132, but there's not much to do unless we figure out how to replicate the issue--it's possible that it's related to a bug on the LG device's MTP implementation.

In the meantime, can you verify whether wifi sync resolves the problem?

-Rusty

Ratings are not displayed in MMA after I do USB sync of my music collection MMW => MMA, approx 4500 files. Music is synced to external 64GB SD: /storage/external_SD/Music
MMW 4.1.0.1658
MMA 1.0.4.0164
Phone LG E-980 (LG Optimus G Pro), stock Android 4.1.2, kernel 3.4.0, rooted

I did a clean install (removed older MMA version and /storage/sdcard0/MediaMonkey folder with the database, cleaned dalvik cache and cache partition just in case).
I had the same problem with the previous two versions of MMA, since the moment I started using it. Frustrating...