Okey dokey!
First things first: try re-installing the software for the Unicorn HAT HD using curl -sS https://get.pimoroni.com/unicornhathd | bash, making sure that you get the HD version, and not the normal version.
The inherent differences between the packages can be enough to give you real problems! It’s probably a good idea to re-flash your SD card before doing this if it is possible, since it’ll remove any unwanted and potentially malicious software.
For reference, take a peep at this thread over here: Unicorn HAT HD programs not working