Shouldn't we only call postRemovalCallback within this if condition? I don't understand why we'd call it if we haven't removed anything

What's confusing to me is that it appears postRemovalCallback can be called multiple times.

If it gets called multiple times, won't the semaphore wait be concluded on the first time, and then the subsequent times might be missed?

If it's meant to only be called once, then I think it would be good to add a return or something here, to make it more clear to the reader than it's only called once.

I don't understand why we'd call it if we haven't removed anything

I think the naming is bad for this lambda.

Shouldn't we only call postRemovalCallback within this if condition?

This lambda increments zero-valued semaphore that NSE callback is waiting on. If we never execute code inside if statement we might be stuck waiting for the semaphore to be incremented until time-expiration callback fires.
I can imagine a case when user manually removes notification from notification center after rescind arrives but before it starts being processed by NSE. I wanted to avoid it by placing it outside of a conditional.

What's confusing to me is that it appears postRemovalCallback can be called multiple times.

This is my programming mistake. This callback should be fired after for loop scope. This way we call it once and only once.

So the plan is:

1. Change the name of this variable (or just place its code in appropriate place since it is lambda - I extracted this code to lambda for readability.)
2. Call it just after the for loop.