Unable to search for usernames that have a period in it and the Profile Visibility is set to Organization when adding users to a group from an external organization.

Workaround

As a workaround, search for the user ID to populate the correct username. Refer to the instructions in this article: https://support.esri.com/en/Technical-Article/000022897.

The example below shows that searching the username using the exact username does not populate the same result:

Steps to Reproduce