Check your TV aspect ratio first, then Emu ones, slowly!
Go to Settings, Common Settings, Browser Settings, Scaling Method. You can then choose between the 2 other options. Exit, restart app. This works for me every time.
I can't say I have ever seen this..perhaps this has to do with surface acceleration
Happened to me before wish I knew how to fix it. I had to switch boxes lol.
Go into your profiles settings, STB configuration, and then change the resolution.
I believe I have used 1280x720 with good results. You'll likely need to restart the emu to see any results.