DIAGNOSIS: The docking system relies on two things: the dock being securely mounted to the wall, and the latch on the back of the vacuum handle engaging correctly with the dock's hook. If either is off, it'll feel loose.
FIX: First, check the wall mount itself. Make sure all the screws are tight and the wall anchors (if you're in drywall) are holding firm. The dock shouldn't wiggle at all. Next, look at the silver latch on the back of the vacuum handle. Press it with your thumb—it should spring back out smoothly. If it's sticky, spray a tiny bit of electronic contact cleaner around its edges and work it in and out. Wipe away any visible dust or grime on both the latch and the dock's hook.
IF THAT DIDN'T WORK: The plastic hook on the dock might be worn or broken. Inspect it for cracks. Also, try docking the vacuum without any attachments. Sometimes the added weight of a clogged cleaner head or wand can put extra stress on the latch, making it seem like it's failing.
HEADS UP: When you dock it, you should hear and feel a definitive *click*. Don't just rest it on the hook; give the body a slight push upwards until it engages. Rushing this is how people wake up to find their vacuum on the floor.