I’ve just run into the exact same problem. I simply solved it by choosing
Sync Project with Gradle Files. This will trigger a Gradle re-import and a build.
As of Android Studio v3.2, the icon is located near the top right tool bar. You can also find it using
Find Action shortcut CtrlShiftA.
You can do the following:
“File > Sync Project with Gradle files” (worked for me)
File > Invalidate Cache & Restart > Just Restart
File > Invalidate Cache & Restart > Invalidate & Restart
Close Project and Re-Import the Project
File -> Sync project with Gradle files