While doing some Android Enterprise enrollment tests for corporate-owned devices with work profiles I stumbled over the following issue after signing-in with the work account: “Page not found”.
The solution is fairly simple, just double check that your user does not have the device enrollment manager role assigned, which can be found under the device enrollment pane: 
The docs tell us:
If you’re enrolling Android Enterprise personally-owned work profile or corporate-owned work profile devices by using a DEM account, there is a limit of 10 devices that can be enrolled per account. Microsoft Docs
In my case, I wasn’t exceeding that limit because it was the first enrollment with that account so I’m not sure if the docs are accurate.
Updated 21.12.2020:
I already opened an issue on GitHub about the doc contents.
@nicolonsky Good question. Using a DEM account isn’t available to enroll COPE devices. We fixed the article. The changes should be live later today. Thanks for bringing this to our attention.
Hope this helps.