J.S.Park sent me this message:
You may know the Sony sensor having phase detection pixel shows banding in strong light. Olympus E-M1 Mark II having such Sony sensor also shows similar phenomenon. Sony camera shows banding while Olympus E-M1 Mark II shows pattern noise. I have thoroughly tested it and posted it in my blog:
I’d like to share my findings.
It appears this is a common issue on all sensor with phase detection pixels. Don’t think there is a workaround yet. And don’t get alarmed because this happens in certain very specific and rare conditions only.