I have received a reply from thomann which is where I bought it and they tell me:
"Thank you for your patience.
We have been able to review the video with our service department.
This seems to be common with Denon products but despite that there doesn’t seem to be a solution as it depends entirely on the CPU usage.
We are sorry we are unable to help you. Our only suggestion would be to contact the brand’s support directly.
We appreciate your understanding."