.background is probably not what we want - this qos may have long delays,
apple is a bit opaque in its description,
but stackoverflow is pretty concrete (https://stackoverflow.com/questions/53141829/performance-of-background-queue-in-swift)
and we even have a comment in our code ("may be delayed by tens of minutes").

this also fixes the warning
"Thread running at User-initiated quality-of-service class waiting on a lower QoS thread"
as before the background was .default while the event handler was .backgound

potentially, this change could explain several issues :)