OK, so I have had a reply from Steinberg Support (it took 18 days) and, so far, things seem fixed. If it helps anyone else here’s a copy of their reply…
If you have not already done it, I suggest downloading the latest Cubase Pro 13.0.20 update, which is available by opening the Steinberg Download Assistant
(I already had 13.0.20 installed so this can’t be the solution)You should also try to change the hard disc location where the project is saved.
(I was working from a reliable external TB3 drive that had not given me any trouble previously)You should reset your program preferences by generating a new preferences folder.
In order to do so you must rename the folder mentioned below. Note that since Mac OS X 10.7.x the user library is hidden. To access it, please click on the “Go” menu in the menu bar of the Finder. When the “Go” drop down menu appears, you need to press and hold the key “alt” on your keyboard which adds the “Library” entry to the menu.Now please rename
“/Users//Library/Preferences/Cubase 13”
to
“/Users//Library/Preferences/x_Cubase 13”Important: If you find folders of previous program versions, make sure to hide or remove them too.
Preferences that have taken a lot of time to configure - the key commands for instance - can be copied from the inactive folder to the newly created active preferences folder at a later point.
More details on the preferences can be found here:
https://helpcenter.steinberg.de/hc/en-us/articles/115000245510-Preferences-of-Cubase-and-NuendoPlease let me know if you need Steinberg Technical Support’s assistance again.
Best Regards
Steinberg Technical Support Representative
Now I can’t be sure which of the above fixed the problems, but one thing I should have guessed was that my previous Cubase installs (pro 11 and pro 12) were being accessed for preferences when I removed the Cubase 13 folder. So maybe it was that all along.
I have to say though that I was having no problems doing the same things in Cubase pro 12. Could it be that simply allowing new installs to access older version prefs files is a bad idea? Moving forward I will create new, clean prefs on upgrade installs and then manually copy my key commands etc. back into the appropriate folders.