Diagnosis
Latch mechanism failure. The plastic locking tabs on the hose end or the receiver port on the vacuum body are worn or broken.
How to Fix It
Inspect the gray plastic collar on the hose end. There are two locking tabs. Ensure they are not cracked or missing. Press the collar's release buttons and push the hose end firmly into the vacuum's rear port until you hear a distinct click. The tabs should lock over the ridge on the port.
If That Didn't Work
The receiver port on the vacuum body may have a cracked or damaged ridge. This requires replacement of the entire rear housing assembly. The hose end collar (part #0423C) can be purchased separately if only its tabs are broken.
Heads Up
Do not use duct tape as a permanent fix. It will not hold pressure and allows dirt to bypass the filtration system, sending debris directly into the motor.