Does anyone ever lose lucidity in a dream but you still think you're lucid until the dream ends?

As in you lose lucidity, but you still think you're lucid while inside the dream.

However when you look back on it from a waking perspective you realise you lose lucidity somewhere in the dream, because from that point on you do stuff you would never do and your dream once again becomes completely illogical with disconnected events.

For example, in yesterday's lucid dream I decided to debate a dream character, don't even remember what it was about. Debating a dream character is a valid thing to do, but it's not something that I would personally do, I see it as a waste of time that could be used shooting lasers or doing other cool stuff. The dream also became very convoluted as dreams, but not lucid dreams, usually are. I definitely lost lucidity. However in the dream I 'thought' I was still lucid and still had (diminished) superpowers. I also helped my mom with tech support which I obviously wouldn't do if I were lucid.

How do you prevent this? Perform more reality checks to reaffirm yourself?

This is called mind wandering. You lose motivation to do lucid dreaming related stuff during the dream, so your mind wanders to other things. This can happen if you fail your dream goals, or if something in the dream otherwise interests you more than your dream goal.

To prevent this, you come up with a plan for what you are going to do if your initial dream goal fails, or you make a point of being aware of your mind wandering during the dream in the future. Think about what you think you should have done during the dream and try to do that next time you find yourself losing motivation to attempt your dream goal.