UPDATE on this… Support got back to me and gave me a workaround for the page loading issue that works just fine. It meant deleting and rebuilding the Pro gallery on the home page which was annoying but it worked so that was a relief. They assure me devs are working to fix this.
I also found out why the menu was not functioning properly on mobile. Somehow the icon had got set to 0% height. I’m guessing this happened around the time of an earlier issue where the header and footer suddenly appeared in the middle of the page rather than the top/bottom, an issue that appeared to be fixed quite quickly.
The icon was set to the right width and this was enough to display it within the header but its container, being set to 0% height meant it couldn’t be selected and caused it to disappear all together on ‘close’.
Resetting both height and width set pixel values sorted the problem out although it took me a while to realise that was the problem as the icon was visible and kind of functioning inspite of the 0% setting.
I now feel my site is functioning as I expect and feel satisfied that I can now concentrate on refining the design and UX.