OneDrive, Monterey and Vanished Files

I have two OneDrive accounts and I was planning on shutting one O365 account down.

Before doing that I started copying my files from one of the OneDrive folders on my Mac with another OneDrive folder on the same MacAir running Monterey 12.1.

Partially through one folder transfer, finder crashed and on relaunch, things got odd.

Only one of the OneDrive accounts would load up, however, the second OneDrive account saying the start application could not open.

And it wouldn't let me transfer files anymore.

It would let me download the files to an external drive, so I started that process. As there was over 500Gb of data, this ran over night.

This morning I awoke to a radically changed environment - both OneDrive accounts hold the exact same data now. Sadly it is the data from the destination account which is only a portion of the files. The source account, its folder is gone and seemingly the files that were in it.

This is true of the online cloud versions as well.

The files were there last evening because I was working on some of them in a folder that in the source account, wasn't being downloaded at all.

Nothing in Trash on the system nor in the Recycle bins of the two OneDrive accounts.

Devastated that about 300GB has just vanished.

Weird part? the folder structure is intact, just files missing. Some folder it's all of them, others, it's just a portion.