Anyone who receives tasks requests in Outlook 2016 and attempts to send a status update already knows about this bug: the status update does not include an address in the To field. Accepting and declining a task should work as expected while marking the task complete returns an error mess that it doesn't know who to send it to, but sends the Task Completed notification to the person who assigned the task to you anyway. Status update messages are missing an email address in the To field.
We need to know who to send this to. Make sure you enter at least one address
Clicking the Send Status Report button will open a new message form with a blank To field.
There is no workaround to use while we wait for this to be fixed. Users will need to click OK on the warning dialog and enter an address when they send a status update.