Hello,
difficult to say... maybe you can provide an image that shows the issue.
Maybe, this could happen if the new screen content contains a transparent background so that there is undefined content after the composition of the new screen.
Can you check the macro EW_PERFORM_FULL_SCREEN_UPDATE in your ewconfig.h? Does the behavior change when you set this to 1?
Does the issue happens also on the reference hardware with the official touch display?
Best regards,
Manfred