2.24.22 UPDATE: We've been listening to your feedback, and we've made some design changes. We're releasing a new version that addresses the most common themes and makes it easier to achieve the previ...
Updated Feb 24, 2022
Version 12.0
Blog Post
Here's a new problem. I mean the problem is new to me--perhaps someone else has hit this and posted above--if so I haven't noticed.
Some of my aliases (7%?) point to the cache folder instead of the sync root. This include aliases that I haven't touched or used for years. So presumably this happened in the blindside conversion, and hopefully will never happen again.
Fortunately I only have 266 aliases on my drive. I've turned on the inspector and am going through them one-by-one and fixing the problematic ones—about ten so far and I'm halfway through. I would never have noticed but I opened a spreadsheet through an alias and noticed Autosave was off. So I saved manually and investigated. The save had gone to the cache folder. When I opened the original from the sync folder it did not have the changes. That's the sort of error that might not be caught for a long long time, and the new file would not have backed up--not locally using Time Machine, and not using OneDrive either (at least not in a predictable way).
To go through your aliases do a Finder search on "kind: alias" (without the quotes). Choose "This Mac". Select the first file and choose File Inspector from the File menu. You might have to hold the Option key down to see it. Now you can arrow down through your aliases, correcting the damage Microsoft has done as you go. If you see "UBF8T346G9" (or similar) anywhere in the Original path you'll need to click the Select New Original... button and choose the file in the new normal OneDrive path.