Hi Jerrel den Harder& thx for join me here at Q&A portal,
an Azure DevOps identity visibility issue, not a Git permission issue. Since they can create branches, push, and open PRs, repo permissions are probably fine. The broken part is the identity picker. Project-Scoped Users is very likely involved here. That group intentionally limits what users can see outside their project, and external users often hit weird identity lookup limits bc of that. Classic Azure DevOps: permissions say yes, identity picker says 'never heard of them' :))))))).
try to add one affected external user directly to the project team or Contributors group, not only through an Entra security group. See if Limit user visibility and collaboration to specific projects is enabled at org level. Try adding the reviewer by email / unique identity instead of display name. Look the reviewer has already signed in to the Azure DevOps org at least once. If direct project membership fixes it, then the issue is the combination of external users + project-scoped visibility + Entra group-based assignment. If it still fails, I’d raise it with Azure DevOps support, bc the identity picker behavior is service-side.
rgds,
Alex &
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