I have an app (here) that, among other features, allows to share APK files.
In order to do so, it reaches the file by accessing the path of pack
For me instant run was a nightmare, 2-5 minute build times, and maddeningly often, recent changes were not included in builds. I highly recommend disabling instant run and adding this line to gradle.properties:
android.enableBuildCache=true
First build often takes some time for large projects (1-2mins), but after it's cached subsequent builds are usually lightnight fast (<10secs).
Got this tip from reddit user /u/QuestionsEverythang which has saved me SO much hassling around with instant run!