I think it's something else.
The ASI533 can absolutely suffer from the rolling sensor read-out, but only during very short exposures.
And usually, when the image signal has a different refresh rate, imagine the LEDs from a flat panel refreshing at a different rate. And then you can see some diagonal banding in your flats, But only mildly and at different places in the image every time.
Looking at the consistency, this to me looks a lot more like a shadow is forming somewhere in your imagetrain.
For reference here are some examples of my shortest flats hyperstretched in PixInsight:
All the way on the left my very shortest flat 0.012 sec. You can see a hint of banding due to the LEDs in my panel refreshing before the image was done.
In the middle 0.014 sec. I'ts completely gone.
On the right a way longer flat frame 19 secs. For when I use my L-Extreme filter.
