I was out for a few hours last night with the 800mm Newtonian, mostly to test out the focuser setup and get autofocus working with the AF3. I got about halfway through that--I think I have backlash accounted for, but still had some weirdness with the AF routing, and thinking that was the tension screw on the GSO focuser being too loose. In the middle of testing I kept running into wide bands of reflected light that changed from target to target--I jumped around to NGC 1499, Witches Head in Orion, and last, M45, the Pleiades. There were bands of light of various directions for all but the Witches Head, which is the only one in the southern sky.
Spent the day shooting dark frames and covering up various parts of the scope to track down the source of unwanted light. (I remember Cuiv had a video on this a while back, with a similar issue with his Vixen 800mm Newt). I now have a black cloth sleeve that rolls up from the focuser base to the camera. It works, and it doesn't even look that weird. Really.
Here's an example of 30 stacked subs of M45, no cal frames, with the band of bad light diagonally across the center--sort of reddish with RGB lined up. I didn't even try to stretch the image, just wanted to see how much showed up after stacking. And the real issue here is that this changed with targets, so no extracting it with flats.
Update: I'm now wondering if my Wyze cam with the IR lights was part or all of the problem. It's one of the Wyze Cam 3s with pretty good low-light video. I usually don't run it with in night vision mode with the IR lights, but I was this time.