Upgrade Android studio version to 3 or more. this bug is resolved.
This was a bug on version 2.0 instant run and issues were reported check these links
https://code.google.com/p/android/issues/detail?id=199884 https://code.google.com/p/android/issues/detail?id=195062
https://code.google.com/p/android/issues/detail?id=206698
https://code.google.com/p/android/issues/detail?id=209413
https://code.google.com/p/android/issues/detail?id=206627
thing to do would be to disable Instant Run entirely by
Settings > Build, Execution, Deployment > Instant Run > Enable
Instant Run
You can file a bug at this link: Google Issue Tracker
please check this answer https://stackoverflow.com/a/35169716/2826147 to turn it off.