AU UI Problem
Firstly, I m using Mixbus in case that has any relevance to this problem. I could try original Ardour but I don't see how this could be a Mixbus only problem. I am using a Macbook Pro 2008 model.
When I have AU UIs open and open another Ardour project I am left with white squares where the AUs UIs were. This is permanent across any app on the desktop until I shut down Ardour. It happens with all plugins.