Generics compile errors in Kotlin 1.4 vs 1.3

Question

I have the following code (here is the link to the Kotlin Playground):

import kotlinx.coroutines.*

sealed class CallResult<out T : Any> {
    data class Success<out T : Any>(val data: T) : CallResult<T>()
    data class Failure(val error: String) : CallResult<Nothing>()
}

public data class Response<T>(val body: T?)

suspend fun <T : Any> f1(lambda: suspend () -> Response<T>): T = when(val result = f3(lambda())) {
    is CallResult.Success -> result.data
    is CallResult.Failure -> throw Exception()
}

fun <T : Any> f3(response: Response<T>): CallResult<T> {
    val body = response.body
    if (body != null) {
        return CallResult.Success(body)
    } else {
        return CallResult.Failure("error")
    }
}

fun f4(): Response<Any> {
    return Response(Any())
}

fun main() {

    GlobalScope.launch {
        f1 { f4() }
    }

    print("done!")

}

This code compiles and works fine in Kotlin 1.3.72 but gives the following compile errors in Kotlin 1.4.30, saying that f4() cannot be called in f1:

Type mismatch: inferred type is Response<Any> but Response<Unit> was expected
Type mismatch: inferred type is Any but Unit was expected

Fun fact: this happens only when it is the last call in a lambda (making it a return result), otherwise it compiles also in 1.4:

    GlobalScope.launch {
        f1 { f4() }
        print("test") // adding this makes it compile in 1.4
    }

Can someone explain me what changes in 1.4 caused this to start failing to compile?