Well, it turns out that no, disabling auto-backup did not actually remove the issue. I will now disable Auto-save and see if that helps. (I'm still suspecting the 'Auto' features. I have Auto-save set to 'Hourly', and I have just come back a little after an hour to save my project. The Auto-save will kick in if there's activity in C2, and it so happens that my first command was to save the project.)
@Ashley, I know that this is a highly irregular bug and it might be something to do with the file system (I've had my own code demons dealing with stuff like this). But in the hopes of finding a workaround to make the save function work reliably I took a screencap of the latest 'hang':
On the status bar it stops at Saving project settings. I noticed that the uistate.xml was successful in saving the latest, but unfortunately, the .caproj did not save.
Perhaps there is a workaround to bypass certain procedures and simply get on with saving the 'essential' stuff, like the events? It's just that I'm sometimes losing a lot of progress and it's quite unnerving to know that my previous successful save might be my last. FWIW, I'm using a local drive; I run as Administrator in my machine. Again, I am looking at disabling Auto-save, and hopefully that works. Thanks for reading.
@SecondDimension, now that you mention it, it does seem that it started happening when I upgraded from r250 to r256 recently. Of course, this has been happening before, but I concede that when it did happen I was also using cloud storage (both Dropbox and OneDrive in separate instances). And I don't recall this happening since I started this project last year, and I've been on r250 for a long time before upgrading. I don't mind downgrading, though I'll be darned if that's the reason.
But like I said, I'll switch off Auto-save, and see what happens.