I just did a quick test and could build promptinvasion and run it on an emulator OK.
I updated android studio and all my sdk bits in the process to:
Android Studio 3.1
Android SDK Build-Tools 28-rc1 (actually have lots of these installed)
Android SDK Tools 26.1.1
NDK 16.1.4479499
But in general, gradle *can* cause issues, usually just after upgrading android studio although this time it ‘just worked’ (for the first time ever I think). I usually end up fixing problems like this by just trying random things in android studio and googling. There do seem to be 2 ‘versions’ of gradle involved – gradle itself and a gradle wrapper for android studio – both of which seem to have their own version numbers so it gets hella confusing.
Also, the emulators appear to be fairly broken with the latest update – I can run stuff on them but there is resizing/snapshot weirdness.