Actually technically speaking I believe it's sorting files by the track numbers in the tags - I did some messing around with this when they fixed it (not actually a recent fix, but it was an easy one to miss), and I seem to recall that if you remove the leading numbers from the file names the tracks still show up in track order according to the numbers in the tags. I could be remembering my experimentation and the results wrong though. But still, whatever, it's still a pretty big win in the "please tesla fix this" realm!
Edit: ignore that part above - I redid my little experiment, and You Are Correct® and I had indeed misremembered. It is indeed sorting by file names - if you have a leading number in the file name all is good. It is then displaying the track name that is in the tag, not the rest of the name in the file name. This is all correct behavior, Yay!
Oh, and I reran another little test - I've been collecting files that didn't play all the way to the end, but were cut off 2-5 seconds before they were supposed to. I had them in a dropbox that I shared with tesla. All of those files now play correctly, all the way to the end. Another Yay!
Oh, and...
Sorry for being a model 3 owner poking into a model S thread, but... is the resume after power cycle thing still broken on model S's, or does it at least work as I described it a few posts up?
My issue (at the moment) is numerous repeated entries of the same album name in the album list, apparently one entry for each song in certain albums (not all). Can someone state what tesla's current logic is for indexing albums? is it some combination of album name and some other field, that causes the multiple entries? It seems to happen mostly with mixes with multiple artists...