There were some issues reported about people getting problem with SharePoint credentials after takeing-over other's dataflow, or after importing dataflow (json) (*). I have the same issue and found out the issue is with condition:
"Each user can only have one set of credentials per data source, across all of the datasets they own, regardless of the workspaces where the datasets reside."
The problem is, even with the same source (SharePoint site), but if use has already establised the connection to the same SharePoint but different case sensitive then the they will get problem with source credentials.
I found that, saved credentials differentiate between:
If you would like to suggest some feature improvements. I have found users with similar needs to you here
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