I'm not one of our Focus users, so I am unsure of the version, but I do have some positive news to share.
This weekend, I was finally escalated to SIS L2 and had a tech there who was helpful. They are having the engineers look at the issue with multiple due dates not allowing sync, but in the meantime, he let me know that a remaster of the gradebook will send the scores. He was right, and when I remastered, the scores completed for that teacher. We were able to verify, in Focus, that the grades were there.
Additionally, he enabled the ability to sync differentiated assignments. This should allow some students to be assigned to an assignment even if the entire section isn't assigned. It will send the others are "excused" to Focus. I don't believe this was "ready" yet, but he enabled it early for us since we discussed why multiple due dates were important and I think he knew I was beyond upset with the last tech's support. This is likely a "coming soon" that we have early, but I am excited to test it with our next teacher who wants to use this!