why would my OneDrive suddenly be processing over 40,000 changes?

This is happening to me too. Onedrive is accessing my c drive documents folder and syncing everything up to the cloud - even when it was NEVER linked to sync. It is also syncing EVERYTHING on the cloud down to my c drive. I only had 6 folders set to sync. Someone stuffed up an update big time.

I've noticed the same thing on both my desktop and laptop, no significant changes and I have over 200,000 files processing... lol

I came hear looking for an answer to the same question. Just logged into Windows 11 on both my laptop and desktop and OneDrive is processing over 40,000 changes on both of them. I can't tell what is actually happening, no massive change in my OneDrive Recycle Bin for instance. This is concerning.

Update: possible solution - sign out sign in

Okay, here is an update because I got fed up with waiting. I thought I would just try something else on one of the devices I was having trouble with. There are two. Both had something like 200,000 changes at the time of writing, which it was apparently working through. And both had gone up before starting to come down! By the way, both computers have been running since my first post two days ago, and neither has finished despite my best predictions that they would.

Anyway, here's what I've just done, and it seems to have worked. Caveat: I haven't exhaustively reviewed all changes I may have made.

If you have unsynchronised changes, please take a copy of your local OneDrive folder before doing this**. You might remember which files have changed and can just copy these. I plan to use BeyondCompare later to check.**

Steps

1. Right-click the OneDrive icon, click the Settings (gear icon) and go to "Account"
2. Click "Unlink this PC". Confirm the action and pray to your chosen deity.
3. OneDrive will tell you that it is signing out. This took a few minutes on mine.
4. If you look at your OneDrive folder (c:\users[yourlogin]\OneDrive) the local files should still be there. Don't change anything!
5. Go to C: and delete c:\OneDrive.Temp or similar name (I deleted mine so I may have forgotten the exact name)
6. Right-click the OneDrive icon again and now click "Sign in"
7. Enter your email (same one as used before) for the OneDrive account and click Sign in
8. On the next screen "Your OneDrive folder" if you weren't previously using the default location change the location to where your OneDrive files already are.
9. When you click next, it should ask you, "A OneDrive folder already exists on this PC." Click "Use this folder."
10. I skipped the Backup step in favour of reviewing this later.
11. Then click next a bunch more times. Skip the mobile app ****.
12. You should then get "Your OneDrive is ready for you"

Warning! It will now synchronise every folder like the first time you added it. Another issue has been reported for this, and it is also very frustrating. Once it has completed, you can untick some of the folders by clicking the "Choose folders" button under "Account". However, decided I would just let it finish before clicking the Free up disk space button, but you could possibly try it so you don't run out of disk space.

In all, the process took less than 30 minutes. I hope you have the same luck!

TL;DR

Click "Unlink this PC". Then sign back in and select the same folder as before. Hey presto!

I had the same issue a couple of days ago. Suddenly millions of changes being processed and going down super slowly like 2 every second and changes I make during that time weren't syncing, API calls to edit files weren't working.

I decided to reset OneDrive. With that, it seemed to process changes much faster, like hundreds per second instead and it finished within two days I think. After that, I had a few remaining issues:

1. A folder was renamed from "x" to "x-USER" (x being the original folder name and USER being my PC name), as if there is a conflict but only "x-USER" was present while "x" was totally gone. When I tried renaming it back to "x" on my PC, OneDrive would rename it back to "x-USER". When I renamed it on the website, it gave me this error "request was cancelled by event received. If attempting to delete a non-empty folder, it's possible that it's on hold". So what I ended up doing was moving it out of my OneDrive to another folder on my PC, renamed it back to "x", deleted the folder on OneDrive website and copied it back to OneDrive.
2. Same as 1 but not my local folder, a shared folder from someone else that I added. I tried removing the folder from my drive, which was successful, then re-adding it from the shared list, but OneDrive said the folder is already added. So I had to ask the sharer to remove me, deleted the folder from my local PC, re-share the folder to me then I was able to add it back to my OneDrive. However, when it synced to my local PC, instead of being a normal folder that you can see files locally, it became an internet shortcut where when you open the folder, the browser opens to that folder on OneDrive.
3. Two video files were stuck in a download loop (even though those files are already on my PC). It would download and complete and re-start downloading again. I resolved this by moving the file out of OneDrive, deleted it on OneDrive browser and restored it from the recycle bin on OneDrive browser. This time it downloaded once and finished.

Now no changes being processed, files syncing and API calls working as before. Been considering moving to another cloud service for a while now because I've been getting OneDrive sync issues all the time and Microsoft support doesn't seem to be able to help (getting conflicts with word docs and excel spreadsheets or files won't update) and then this issue really pushed it over for me.