After update latest SuiteCRM 7.4 Release Candidate that Assigned to not working. Please see the attachment
We are aware of this issue, It seems to be based around the PHPmailer files.
For now, a workaround will be to go to Admin > Email Settings.
Uncheck the box for “Assignment Notifications”.
This will mean that users won’t get e-mails if a record is assigned to them, but you will regain the functionality to do assign records.