I've managed to isolate this issue. It is still a ...

# coroutines

[nwh]

I've managed to isolate this issue. It is still a complication with crossinline, and it still isn't fixed in coroutines 0.26.1-eap13 and kotlin 1.3.20-dev-165

import kotlinx.coroutines.*

class Handler(val func: suspend (Any) -> Unit)

// Switching crossinline to noinline fixes the error
inline fun createHandler(crossinline handler: suspend (Any) -> Unit): Handler {
	return Handler({ handler.invoke(it) })
}

fun main(args: Array<String>) {
	val exec = newSingleThreadContext("sample")
	var handler: Handler? = null
	
	fun send(obj: Any) = async(exec) {
		handler!!.func.invoke(obj)
	}
	
	handler = createHandler({
		if (it !is String)
			// Removing this launch statement "fixes" the problem as well, but that's a non-solution in some cases
			// Removing await also "fixes" the error
			launch {
				send("Handled $it").await()
			}
	})
	
	// This starts to break around 10 repetitions
	repeat(15) {
		send(123)
	}
	
	// Delay to let events finish
	runBlocking { delay(1000) }
}