I have tried all solution on Can't attach Android Studio's debugger to Android process But still failing to attach.
And then I found out the problem is I switch the Build Variant to release few weeks ago, that's why I could not debug.
Solution: check on your product Build Variant. Usually only debug Build Variant will allow you debug only (If the buildTypes have been set in your project. It can be confirm when you search keyword "buildTypes" in whole project)
