Hi @roryaronson,
Many thanks for all the work that goes into trying to understand what’s going on.
To answer your question, I did try 14.2.1 and every version thereafter. You can see in this thread (July 7, 2021 Software Update) some of the discussions that @RickCarlino and I had around this particular issue.
I am keen to progress this and would gladly accept your kind offer to swap boards. 1.6 would be great 
!!!