I've got an AMIKO VIPER 4K V40

I've tried OpenVix 6.0 and OpenVix 6.1 Willobuild and both seem to have the same issue where occasionally the video image will disappear and go black.
Audio is still working fine when this happens.
Menus still work and appear so this suggests it's not an output/HDMI issue.

Sometimes if I go through various menus it will eventually reappear, or I have to wait a while.
Other times it require a restart to restore the picture.

Has anyone seen this issue before?
Any ideas or advice?