Well, that's good! One of the most difficult tasks in the universe (seemingly) is to keep an Android app from crashing when it runs on a variety of devices. So I'm glad to hear it's being stable.

There's just a huge amount of variance in devices to try and account for.
As for the Selfie's behavior: To my knowledge, everyone's experiencing weird behavior with Selfie on the 3DR app on iOS and Android, and on Solex. When I built the Selfie shot in Solex, it never did work properly, and I looked at the Selfie code on the Solo itself. What it's supposed to do is set an ROI (region of interest) on the location calculated by the gimbal angle/heading/location/altitude, and maintain focus on that as it flies backwards to the designated distance and altitude, then reverse course and fly back. It doesn't do that. It picks an arbitrary location 8 feet or so directly in front of the Solo,
then flies. So it never tracks the actual target like did in earlier versions. To see about fixing it, I modified it to work like an earlier (good) version of Selfie on my particular Solo? The result? My Solo now turns to the north. I screwed it up, but this is
not in Solex. It's in the python code on my Solo.

I've no idea why yours is doing a 180 when you run Selfie. Others have reported the camera jerking to straight ahead position, others report it not doing anything, etc. I haven't gotten to the bottom of it yet, but in the meantime I'd suggest using MPCC in place of a Selfie. It works great, and can do a bunch of other things besides, as you probably well know.
On the Vehicle Settings screen, it pauses for ~1 second before actually trying to write your settings to the Solo. The reason is that if you move a bunch of sliders in rapid succession (or move a single slider back and forth), it "batches" those changes together and writes them all when you've stopped making adjustments. The idea is to avoid trying to write settings constantly, and greatly reduces the chance of something going wrong. What I would suggest is making a few changes and giving it some time, until you see the "X parameters updated" at the bottom of the screen. It displays that message when it's successfully written the changes out.
Thanks,
Kelly