This video you used is a very good and thorough one. Definitely check it out completely and save it for future reference, it's really quite excellent and showed me some stuff I didn't know.
The one Sam linked to is pretty decent, but it falls in the same trap as the first one you linked to: it eyeballs all the positions. It doesn't use the tracking data to actually help you. You can tell by the way he guesstimates the position of the ground plane.
Unaligning and setting the rotation from your tracks is definitely the way to go here.
I'd love to elaborate, but as you've assumed correctly: I have quite a bit of business related appointments the next couple of days, so I can't step by step you through the workflow.
You get some very decent tracks judging from your low solver errors, so you should be able to get nice results. Since you're working inside Resolve I'd look there for clues as to why your media is disappearing. The 'external' Resolve timeline and the 'internal' timeline of the Fusion page don't always play nice with each other.