(2) If you never personally changed the location of your documents folder while still 1803 (either the way I did or the other way), then it must have been 1809 that did it. It must be the default setting for 1809. That is a sad circumstance, considering OneDrive is normally only 5 GB in size. Those with more than that before the move appear to lose it all.
But later in this thread AgingAardvark56 suggested to look in the online OneDrive Recycle Bin to see whether the excess ended up in there. Did you look? Right-click the OneDrive icon, & select "View online".
I did take a look, in the online OneDrive Recycle Bin. There are some files in there, but they are of the type that you would expect. Mainly overwrites for auto save games and such. Not the missing 100GB VM file unfortunately.
Sorry for the loss of your VM file. Not only does it exceed the capacity of a normal OneDrive, but it breaks this rule...
Sync your Documents, Pictures, and Desktop folders with OneDrive
"File exceeds the maximum file size: OneDrive can't sync files over 20 GB. Remove these files from the folder you want to protect and then try again."
Looks like 1809 set it as default to protect the contents of those folders. But the feature couldn't handle it when a rule was broken. And your VM file now swims with the fishes.