Hey there!
I’m honestly not great at debugging this stuff unless I’m in engine but I can at least share my first impression.
First, can you be more clear about the “pause”? Any time I have had Quartz timing issues, it was usually that I was basically doing some code/checks a beat/bar too late so it ended up only changing on the next subscription event.
My idea at first glance is since you’re checking if you’re on beat 4, by queueing the audio maybe it ends up getting prepped late?
I don’t have experience queueing audio in this way so I’m sorry if this isn’t helpful!