Hi Bobbi
It sounds like any of the following
* loose tolerances or ware on the plastic guides holding it in place
* loose release button
* something it runs over pulls on the dust box, and removes it
Check if the fit of the dust box has become looser over time, and if there is a part of the floor that's unlevel and could catch the box, disconnecting it.
If so, consider using a small layer of tape to add some thickness to the mounting points to better hold it in place