Last Activity Date does not = Last Activity Date
Currently the Last Activity Date field is updated if a task is not completed against the record. This is problematic for users who get behind on their tasks (guaranteed this happens a lot) who then wish to view which record they've worked on most recently or which they haven't.
The system seems to think that if a due date for a task is for example "Today at 8am"... and it is now 9am.. then that record has been worked on even though I may not have even logged into HubSpot that morning.
The solution is to remove the automatic tag of activity based on task time and date.. when the system is reviewing the task as a point of reference it should only update the last activity date IF the task has been completed.