Okay, playing around with it some more it seems to be just my template that is the issue (the std AUS templates seem to work okay) and it is something to do with the layouts. Working with my std note and titleblock drawings on my layouts and master layouts (ie dragging them or copying them to a new layout) seems to cause catastrophic crashing. Again there is no issue with my template in V14. I can't think what would be doing it. Many of my title drawings have embedded jpeg logos (I work for various builders so have different titles set up for different clients)but I can't see why that would be a problem.
V12-V27, PC: Ryzen 9 3950X, 64g RAM, RTX5000, Win 11