I'll do that tomorrow (reinstall).
Some additional details from today.
First off, I tested with my iPad, and I got the exact same results. So, I'm fairly certain it isn't just a corrupted installation. I'm going to give it a shot deleting/reinstalling on my phone anyway, just to be sure, but... They were both installed independently from the App Store directly on the devices, not using iTunes (where one corrupt download could have impacted both), so... I'm skeptical that will help at all.
However... Testing on my iPad provided a pretty essential clue, because of the different UI.
The issue happens when the cover art loads. If I play songs that have no cover art, it is
fine. I can play multiple songs and everything works perfectly. However, as soon as I play a song that contains cover art, it plays fine
until the cover art appears in JRemote (on the iPad you can see it on the bottom controller), and then the whole app is stuck. Like I said, I can still navigate around (though it gets pretty "crashy"), but nothing else will play at all until I force it to close and restart.
The music
always stops just as the cover art appears down in the bottom controller. I hadn't seen this because on my iPhone, you don't see the cover art until you move to Playing Now. The problem is that for this few seconds (apparently while it is downloading the cover art) the app is frozen completely. It doesn't "unfreeze" until the music stops (upon which, you can move to the Playing Now screen, but the cover art was already there then, so I never connected the two things until I tried it on my iPad).
But I was suspicious this morning, because I tried it on the way in this morning, and it seemed to be working fine. Just happened that the album I picked had no cover art, but I didn't connect the two! Now, in testing further, it doesn't seem "universal". It is probably "big" cover art, or something. But I have enough of them that despite trying all sorts of tracks, I never stumbled across one that "worked" yesterday. But, today, knowing to look at cover art, I've now been able to find some tracks in my library that will play fine, despite having cover art (they probably have much lower-resolution art).
And, again, this seems to only happen when connected remotely to my server. The tracks I tested last night at home over WiFi, where the exact same tracks that continue to be troublesome today.
But, hopefully this helps. It is something in the way you are downloading and processing cover art. Again, PM me and I'm happy to send you my server details and you can try it yourself whenever you want.
Also, the cover art download process seems to be what is causing the UI non-responsiveness I described above. When I play a song that has cover art, but still "works" right, the UI still freezes completely as playback starts. You can hear the music, but the counter doesn't count, and no buttons do anything at all. Then it "unsticks" just as the cover art pops up in the little corner display (at the same point where it would normally stop playing with most of my tracks).
And, lastly, the fact that it can't "continue" once it has gotten into this state, seems to be related to that cover art as well. So, for example, on my iPad, I went in and played a song that I know triggers it. It played for 9 seconds, then got stuck just as the cover art popped up in the controller. So, I then navigated and chose a song that has no cover art at all. The little controller shows the right track info, but won't start playing, and the old cover art stays showing.