I had the same problem. After trying numerous methods that didn’t work, I realized that I had accidentally changed an option in my “Run Configuration”. Here’s exactly what I did to fix the issue.
- Run –> Edit Configurations
- With your configuration selected on the left panel (mine says “app”), in the General tab on the right panel, there is a section called “Before launch”. This section should have an option added called “Gradle-aware Make”, but I had accidentally removed it.
- I re-added it by pressing the “+”, then clicking OK in the popup (leave the input box in the popup blank).
- Click apply.
This fixed the problem immediately. Hope this helps someone!
Run / Debug Configurations / Miscellaneous TAB
 Uncheck: Skip installation if APK has not changed
Android Studio doesn’t always detect small changes in code.
The behaviour is erratic. I solved it by reviewing my code.It turned out that there was a resource file that was invalid. Try reverting back to the last working version of your code before the current changes… Probably a known issue that will be/was resolved out of Beta