I spent some time on chat with a Microsoft technician yesterday.
I told them the steps I've been through. They then went on to remove Microsoft office and re-install (which I said I had already done). Because the issue is intermittent, it wasn't happening while they were viewing my screen, so they had assumed it was resolved.
Later on it was happening again. I will re-open that case and hopefully when they realise its not getting fixed, it will raise awareness within support.
FYI: It's an intermittent issue which is hard to replicate. One thing I've found which can often get it to occur is if you are in the presentation mode, if you switch between screens (for my setup this is swiping with four fingers). When you return to the
presentation, the flickering often re-occurs. Just in case you need to show the issue occurring to a technician yourself, or need to be aware of this to minimise the risk of it happening to you.