When there is a user who is a member of multiple agile teams, the user gets a "No matches found" message when trying to change their group on the agile board.
This issue is not reproducible out of the box in the base system in Madrid or New York.
I then New York Demo data, there are six groups which are Type = Agile Team:
User Aileen Mottern (Product Owner) belongs to two groups of type: Agile Team:
The dictionary entry Type on the sys_user_group table was changed from List to Reference.
The issue was reproduced on the Agile Board in the base system by changing the Type from List to Reference on the Dictionary Entry: Type (on sys_user_group table) thereby confirming that this is the issue.
Reverting the change fixed the issue.
NOTE: Review KB0721363 if unable to modify the dictionary entry.