Android Studio Build: Android Studio 4.1 Canary 8
Version of Gradle Plugin: 4.1.0-alpha08
Version of Gradle: 6.3
Version of Java: Java 11
OS: macOS 10.15.4

Steps to Reproduce:

Add the following snippet:

Crossfade<Int?>(current = null) {
  Box(
    backgroundColor = Color.Yellow,
    modifier = Modifier.fillMaxHeight() + Modifier.fillMaxWidth()
  )
}

Run

Expected: A yellow screen
Actual: A white screen
Additional notes:
You can fix the issue by passing 1 as the current state for Crossfade

Description:
If you pass null as the initial state to Crossfade it doesn't compose properly and a white screen is shown.

The reason is the statement if (current != state.current) which fails since state.current default to null.

Crossfade needs to use a sentinel value instead of null as it's internal default value or make the type parameter T non null to prevent this issue.