When I tried to assign a task to a people/Group custom filed via SharePoint designer workflow.
After running the workflow,I found out it suspended in the assign a task action for this user.
This problem might occur because of allowing Multiple Selections for a People and Group custom field in Additional Column settings.
- Open List settings > Below Columns > Click on your people and group column to open its settings.
- In Additional Column settings. > Below Allow multiple selections > Set it to No.
Note: If you need to assign a task to multiple users, you should use start task action rather than assign task action.