With Jira it is now possible to set the use of the Project Lead as the default assignee, rather than everything defaulting to unassigned.
Jira Software for Teams does not seem to check this setting and instead just uses unassigned.
The result is that when combined with the limited filtering options within the MS Teams view things get lost. Even a simple personal TODO list becomes a problem as a user will select the "Assigned to me" filter, while at times will create entries assigned to unassigned.