On my fresh Windows 10 installation, I had OneDrive, OneDrive for Business and Dropbox.
I was able to see only the Dropbox icons, but not the OneDrive ones.
The solution is to go to the registry settings under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers and ensure that there are max 15 entries.
In my case I had this:
So in my case I have delete the Dropbox icons, and now I can see the OneDrive sync status.
taking inspiration from the blog post Managing overlay icons for Dropbox and TortoiseSVN and TortoiseGit, I see that the best solution is to keep the important icons for both OneDrive, OneDrive for Business and DropBox (for DropBox, I keep the icons 1, 2, 5, and 7). So in total I have now 14 entries, and I should be fine.
My registry settings now are: