I've been having an issue with converting my music to MP3 for use on an Android device in my car. The device in question is one that installs inline with the factory infotainment and uses the factory screen for display, allowing you to switch between the factory infotainment and Android functionality. This serves as a way to add Apple CarPlay / Android Auto AND the ability to run pretty much any Android app. It is running Android 8, has 4GB of RAM, 64GB of storage built in, the ability to add a microSD card for storage and also has 2 USB ports for adding additional storage, and for providing other ways to connect to the Internet other than a WiFi personal hotspot connection to a smartphone (which is handy as you can't simultaneously use CarPlay and Personal Hotspot on an iPhone). I'm using a cellular router with Ethernet ports and an Ethernet to USB adapter to provide Internet access to the device. I've also got a 512GB microSD card plugged into the device and a 512GB USB thumb drive connected to one of the USB ports to give me plenty of storage for now (and I can easily add additional USB storage later if needed).
I've used the export feature in JRiver to convert my music collection from a mix of (mostly) Flac, MP3, and a few other types to all high bitrate MP3 and then copied the exported files onto the USB thumb drive. I have spot checked a bunch of files using MP3Tag to verify all the tags are present and everything looks correct.
In my quest to find a good music player for Android that has a skin that's usable while driving, I've found a rather mixed bag of results. A few players crash on the Android device every time I try to play a song, so those options are ruled out (MediaMonkey is one of these). A few players implement their own tagging database, but have very poor or no smart playlist functionality. And then a few players use the built-in Android media library to maintain the music database.
The players that implement their own tagging database seem to read my library in just fine, so the lists of artists, album artists, albums, genres, and so on all appear to be properly indexed.
The players that use the Android media library have issues in that they end up having every artist / album artist tagged as "unknown artist".
My exported library has just have 10,000 songs and each file has album art embedded inside.
I don't believe this is a JRiver issue unless the exported tags are being written in a way that Android is unhappy with (a tagging version it doesn't like, perhaps), but I'm hoping someone on here has run into this and has figured out a solution. My searches elsewhere seem to come up with plenty of other people who have run into the same issue, but very little in the way of solutions. One solution someone found was to make sure album art isn't too big. I tried resizing the album art in MP3Tag, clearing the cache on the device, and then having it rescan the music, but there was no difference in the outcome.
FWIW, my Samsung Galaxy S8, which has a more recent version of Android and is obviously a much more standard Android device seems to have the same issue.