Well stated.Lighting is very important, but also the type of flooring in your house. I can't fly / control my Tello in certain rooms in my house. These rooms have solid colored carpeting. But other rooms, with the same lighting, that have hardwood and tile flooring, the Tello is much more stable. Check out the Tello User Manual VSP (page 7) or TelloFPV App Manual VPS (page 11), if you have that app. If you don't have that app, get it, it's amazing.
It's not just you, Tello has it's idiosyncrasies... some of which, I do not understand why. But once you learn them all and get used to it, it's still a lot of fun!... and probably the most stable indoor drone on the market ATM (given enough lighting and 'patterns' for the downward camera to look at LOL)they did help me to know it's not just me or the drone.
It may be just perception issues. The bottom positioning camera probaly has a fixed apeture and frame rate, and could not detect the patterns on the floor to position itself. It would not hurt to turn on the light , unless you are living in 1880 with incandescent bulbs.