I am tempted, not just by your reward, but also by my curiosity. I’m still busy but I have some hope of fixing this relatively quickly. 
But before committing to this I would need to make sure I can reproduce it here in my dev environment. I’m running 8.4.1.
Can you please give me a complete list of steps to re-create on a clean system. I mean everything, from the creation of Quotes, fields, templates, etc. I would love to have this very detailed, as in “click here”, “go there”, “paste this”, etc. I want to have a case that is exactly like the one you’re using in your tests there.