Could you point out the issue here?

Why does async make it harder to reason about when resources are released?

Basically it’s the non-linear execution flow creating situations which are harder to reason about. Here’s an example I’m trying to help a Node team fix right now: something is blocking the main loop long enough that some of the API calls made in various places are timing out or getting auth errors due to the signature expiring between when the request was prepared and when it is actually dispatched because that’s sporadically tend of seconds instead of milliseconds. Because it’s all async calls, there are hundreds of places which have to be checked whereas if it was threaded this class of error either wouldn’t be possible or would be limited to the same thread or an explicit synchronization primitive for something like a concurrency limit on the number of simultaneous HTTP requests to a given target. Also, the call stack and other context is unhelpful until you put effort into observability for everything because you need to know what happened between hitting await and the exception deep in code which doesn’t share a call stack.

Because async usually means you've stopped having "call stack" as a useful abstraction.