Makes total sense. Except in coming here, you are not addressing Apple. Cognizant Apple employees do NOT participate on this user to user only forum, with the exception of Forum Hosts who monitor the forum for violation of terms of use. If you think you're getting the attention here, you're not. Apple is not going to investigate or debug or fix anything because you posted anything here. You need to let Apple know you're having an issue by either contacting Apple Support or using this link to provide feedback directly to Apple --> Feedback - iPad - Apple
In fact anyone who is having this issue should contact Apple directly AND provide feedback using the link I put above.
Now, since this is not a universal issue effecting all Magic Keyboard owners, I'd say it's not a software issue. If it was, just about every user would have the same problem because we all are using the same iPadOS. So, that leaves environmental or accessory caused issues or an actual hardware issue with some keyboards. This is why I asked if anyone is using a full screen protector, which no one has answered. You have to remember the Back Lights are controlled by the Ambient Light Sensor built into the iPad Screen. If the sensor is blocked, it will communicate to the keyboard it's dark and the lights should be on.
If you lock your iPad screen, the back lights should go out regardless. Do they on your keyboard if you actually lock your screen?