Same here. Had to "downgrade" to go back to our previous plan as well.
They also tried to change my country to charge me more, since my original plan is in Canada but I am currently physically in Europe, very odd behavior since my billing is all Canadian.
I noticed the issue affects large folders that make me blow up my 1 TB limit and that OneDrive App removed my local copy of my own "self shared" files from a secondary account while trying to reupload them by creating the same folders with the machine's name at the end.
That would surely not work, since I'd not have enough space, then I am almost sure I'd be presented with a pop up upselling extra TB for a fee.
I have my subscription, like many others, because of the cloud services. Otherwise, we can just use open source alternatives for free.
Funny the problem didn't affect small folders shared with me that only have a handful of GB each. Only the three largest ones that have a few GB were "converted".
I tried disconnecting my account and re-adding it while using the same location, since removing the shares and reinviting didn't work.
Two folders I reinvited myself to showed up on the folder selection, we'll see what happens now, OneDrive is processing almost half million changes, as I readded my account, so it might take me days to see any changes. Hopefully I can get ahold of my files again and update my usb hard drives, good thing this failed, so we remember that backups are our best friend. 🙏🏻