Maybe solved. Complete the objectives in chronological order. I skipped the Optional (take the path set out by) and went right for the scav leader. I was still able to walk through the door, but it never marked complete.
Reloaded and made sure to hit the path your partner prompts. Once it's checked, you can take the scav leader out in anyway you'd like, it will show completed.
When in doubt just do them in order, jumping around or bypassing objectives seems to create problems.