* I have rephrased the post since originally posted *
When I try to run a just-built release apk, I get an error "the apk for your currently selected variant ... is not signed." This is in the Edit Configuration popup. Here are my steps:
So, why this error? The APK generated appears to be valid. I have successfully posted it to the Android Store (alpha testing only) and verified that stack dumps are obfuscated.
What I can't do is download it (step 6 above) to my device. I guess that's ok since I can download the debug version just fine.
(*) Android Studio defaults the output for the release apk to a higher, presumably more convenient directory. However I find it harder to manage the consistency of generated files when they are scattered about so I prefer all the generated apks in one place.