We use Jira 8.8.0 on site and since the upgrade to that version e-mail is not sent when assigning an issue.
I have tried to use the button Assign and the Assign function 'a', but no e-mail was sent either.
I have tried to give a person only one role in a project and then using the Assign button, but no e-mail was sent.
I am desperate, because our users aren't getting email notitfications when they are assigned issues and it's annoying.