IIRC, when Roon solved some iPad display issues with the underlying cross platform framework last year, this was a side effect. It’s a lot better than the previous behavior, and a quick/transient effect, so I don’t mind it. But I can understand how you might not like it if you hadn’t experienced the prior behavior.
Thank you for your post. Does the app recover from the condition you’ve described, or are you unable to retain landscape mode at all?
If Roon recovers and these visual artifacts are temporary, then you’re encountering a known issue. The team has ongoing work to improve iOS tablet user experience.