[smcin]

> ... aren't issues of motivation unless you are seeking to get them to work overtime to overcome these blockers.

OP: Is their compensation and performance assessment linked to getting things done to your deadlines?

>> even if the milestones are aligned by everyone.

> Everyone agreeing on something doesn't mean that everything is understood or correct.

It could be the tyranny of the collective "we": "We should ship X by date Y". Is everybody clear on their individual deliverable to make that happen? When you do post-mortems after a deadline is missed, does everybody have a different picture of who was depending on who to deliver what? Was the root-cause of that lack of incentive, lack of buy-in, or your communication?