One more short description of how it happened to me, just in case someone in Microsoft wants to fix the problem.
Edited a file on my laptop for weeks, saving periodically. Apparently OneDrive didn't get any of these versions because the file was still open in the editor. Then, looked at the file on my Android phone. Didn't edit or save. Then checked on laptop, was told unable to sync file due to being open in the editor. So I saved the file & closed the editor. Immediately OneDrive overwrote the newest version (on the laptop).
Now if I *had* edited the file on my phone, that file would be the newest version, and this would be right (if I'd not later saved on the laptop, which I did).
However: (1) OneDrive should be backing up my saves of the file, whether the editor was closed or not, (2) At the instant I closed the editor, the (just) saved version was currently the newest, even though OneDrive may have been confused about the mod time on the version it had sent to my phone, & had planned to overwrite the one on my laptop when it could, IT SHOULD HAVE CHECKED THE MOD TIME on the laptop file before overwriting, discovered which was newer, and backed up the new one.
My guess is that this behavior is completely replicable. No excuse to not get a fix.