The tooltip shows the issue key and summary field information and is very useful when the task duration is too short to display both fields.
Hover the pointer over a task to display the tooltip.
User cannot edit task - reason displayed
When a task can't be edited, the reason is provided in the tooltip:
missing permissions
in integration (connected tool)
in a box (a user is a viewer only - can't edit tasks)
The box is closed or archived
the box you're in is closed/archived
you are in a portfolio box but one of its children is closed/archived (the resources module of the portfolio aggregates tasks from all child boxes)
show overall assignment - a task from a different box (overall assignment shows all tasks assigned to a resource. Tasks in the scope of the box you are in can be edited normally. Tasks assigned to the resource in other boxes can't be edited)