Some subscribers are not receiving pushes

Subscribers are not receiving pushes randomly, even with all conditions met, as listed here: Commonly reported WordPress Integration Issues & Fixes. I’m currently on free plan, but my quota usage is at 51% only, approximately 31k active users. What could be?

How did you figure that your subscribers are not getting push notifications?

We did some internal tests with a lot of eligible users. And, as I said, I’m below quota max limit. It should deliver notifications to all active users, isn’t it right?

Yes, ofcourse. Have you looked at notification stats? What do delivery stats show you?