A guest user receives their invite email - but at that point there is nothing for them to do, other than activate their account - as no task has been sent.
You can't send them a task until their account has be activated.
This is not clear. the guest user expects to go from the first email to see what action awaits them. Not activate then wait.
Can we look at a 'one and done' approach, but as a minimum add some content to the email to make it clear.