We have been deleted some stuff from one VSTS project due to some internal reorganization. After doing it we found that some workitems cannot be modified / deleted anymore, if we try to delete them we get a:
Failed to delete work item: 47420. Error Details: TF401232: Work item 53559 does not exist, or you do not have permissions to read it.
47420 is the WorkItem that I have tried to delete, 53559 is a deleted workitem that was a child of this one.
If I open the WorkItem 47420 I see under Related Work the error: Work item not found or no permission to access it.
If I delete the link and save the change I get again:
TF401232: Work item 53559 does not exist, or you do not have permissions to read it.
Any ideas? This is happening with quite a few elements ...

The point is that the workitem showing the error is a workitem in a different project which I don't have access to. I've filled a bug about that:
https://developercommunity.visualstudio.com/content/problem/244033/unable-to-modify-a-workitem-with-links-to-workitem.html