This may have gotten lost with so many posts so I'm repeating it on a new post.
If you try this and it works, please post an update so others will know.
My junk filter started working again and there was 1 activity that happened the day before it was fixed.
I ran and downloaded the rules file from Outlook.com. I didn't find anything in the files (long boring XML code), but my problem went away a day later.
I have no idea if running the diagnostics that creates the report fixed it.
After 3 months of 100% of my inbox going to junk, it's hard to call it a coincidence.
Run report: Settings (gear icon) > Mail > Rules > Scroll down to the very bottom after the last rule on the right pane and there's a text link to run a report. (image below)
