Here's how I attach the connectors with the retaining ring:
-Please lubricate the

with a little oil or grease, but not so much that it ends up in the water.
- Place the retaining ring (into its final position), then firmly press the hose into place, which should be easier due to the lubricating film.
-you hear the correct clicking sound, then the snap of the retaining ring as it engages in its intended position.
In your case, someone probably attached the hose, thought it was properly seated, and pushed the retaining ring into place. However, this sometimes happens, but it's not ideal. The hose may seem to be in place, but over time, it can become loose and 'blow out.'