I have experienced similar things with my H on his mornings to pick up D4. For what it’s worth, he has been a very dedicated, involved dad throughout. That said, I find this kind of thing super triggering. My head always goes to thinking he “slept in” because he’s in bed with someone, and the idea of that making him late to see D3 fills me with rage.
I’ve reacted in a variety of ways to this over time. And my advice is, just don’t. If I could go back, I would not show any reaction at all. Then perhaps in a later convo revisit and let her know that it’s important for your sons sake that you both be consistent and show up for him at the expected time?