While my project compiles fine, the Android Studio IDE (3.1.2) started to behave very strangely. It says

AppCompatActivity

cannot be resolved or “Unnecessary non-null check for [ERROR TYPE]“. Everyrthing that should be imported from

kotlinx.android.sythetic

appears in red. Any ideas? I cannot understand what triggered this. I am trying to use some code of my own from an .aar file, but this seemed to work fine. (Invalidate caches etc did not fix anything)

Try building the project

Like I said, it compiles fine. It even installs an APK on my device.

Yes, but usually, compiling with Android Studio also fixes the errors

to be honest man, Android Studio turned into buggy part of the world. For my project where we are developing it just from like 4 months ( 3 people) it builds fast, but when having some caches its impossible to fix those errors. Sometimes Invalidate caches and restard helps, but sometimes i need to reimport whole project from repository. Sad but don't give up and try even those ridicolous solutions.