DevOps Basic User Permissions Issue

Issue: In Microsoft Azure DevOps, external users (from our domain) that have "Basic" user licenses are unable to assign issues to other team members or tag people (by searching for their names) in the Discussion text area.  When trying to assign work items to other team members, they get the message "No identities found" and they are unable to type in that field.  When tagging people in the discussion area, they receive the message "sign-in required" when searching for names (even though they are signed in).  I believe this is some sort of permissions issue but am unsure how to solve.  Our company domain is tied to our Azure account and Office365 account.  We are adding these external users to our Azure Active Users section, so their account names are theirname@ourdomainname.onmicrosoft.com.  They use this to log into sharepoint and our DevOps platform.  This issue does not happen with users within our domain, which makes me believe it is a permissions issue or AD issue.  I searched google for this error and see lots of posts about how the reason you can't search for names is that you have to type their names and then it will take a minute to search AD and find their name.  That is not the case here, so please don't reference those solutions.  If you have any other questions of need further details, please let me know. Thank you!