Loss of abilitys as soon as you realize you're dreaming

Hello everyone. I'm currently trying to learn lucid dreaming. I write down my dreams daily and always make a plan for what I can do once I enter a lucid dream.
I'm not exactly a beginner; I've tried lucid dreaming many times and have gotten used to accepting that I'm dreaming without waking up or feeling excited. I can stay in a lucid dream for a long time (40 minutes is the longest I've ever had).
My only problem is that I can't control the dream at all—no flying, no controlling the light without touching the switch, nothing. Every time I lose hope because I've had more than 20 lucid dreams with absolutely no control, and that's the problem.
In the week before I started again, I noticed that in all my dreams at night I have superpowers like invisibility, flying, stopping time, or performing superhuman feats, and I'm completely unaware that I'm dreaming (I know it's all not real, but I know I have to go along with the scenario without realizing I'm dreaming). But as soon as I check reality or suspect I'm dreaming, I lose all those abilities (if I'm flying, I'll fall, and so on) and I can't get them back.

What's really happening? Why is my brain doing this to me?