Short version: Having an event trigger an UnMute doesn't seem to work if it has a delay set on it. I found a workaround by trigger a secondary event (with delay), and having the secondary event do the UnMute without its own delay.
Long version with context: Our game has a Build Mode where placing objects triggers sounds. When you open a Build project, it triggers the placement sound for all the objects that are already in that project. This could be fixed on the programming side, but we decided doing it on the Wwise side would probably be simpler for now. Our solution was to mute build sounds, open the project, immediately after opening stop all the sounds that were just triggered (in case they're longer), then unmute build sounds. This is how I hoped it would work (I ended up changing the last item to "Post Event" for the secondary event).
Here's the version that worked:
along with this:
