I faced the exact same problem, I was afraid I broke something… I fixed it by cleaning and rebuilding the project (I had disabled instant run as suggested here before but I guess that was not necessary as I enabled it again after cleaning and rebuilding the project and worked just fine…).
Build -> Clean Project
Build -> Rebuild Project
I am not sure if rebuilding would be necessary, I did both steps and it worked fine, maybe just cleaning the project would have been sufficient.
Hope that helps!!
Nice, one more thing. When I solved the problem depicted here I found another problem, when I clicked run the apk was not being created and I solved it with my answer on that other thread:
The APK file does not exist on disk
Disable “Instant Run” Work for me.
Uncheck “Enable Instant Run…….”