Good chance your counter is skipping. It's a common issue in DLS right now. What 'steps per clock' are you running in the settings? Does it still do it if you increase the steps per clock and re-load the chip?
Oh, that would make sense :o Thanks for the response!
I was running with the default settings at 250 steps per clock cycle and 1000 steps per second.
I tried increasing the steps per clock cycle to 500, 1000 and 2000, but all that changed is that the banding pattern changed. I'm wondering if the issue is related to the clock itself... Maybe the screen sometimes updates before the counter, so it gets an old address before the counter has time to give it a new one? With the new speed settings it seems to be a consistent 50/50 if it uses a new or old address, so I feel that might be it?