Further to my previous post, here’s a run down of what happened.
Cyanogen updated from Android 5 Lollipop to Android 6 Marshmallow, which meant after I flashed, I was getting huge numbers of “sorry but xxxx crashed”. I suspected the Gapps was out of date or incompatible with the android version I had, and I was right – a different version was needed. So I flashed that also but that didn’t work, so I rolled back to my last good backup, which was from November 2015, that restored fine, and I’m back to where I was, minus a lot of app changes and updates needed (I uninstalled/reinstalled a lot of apps since that backup), fixed that, reupdated my apps, and redid both my app and my Nandroid backups so I’m good to try again sometime.
I lost a good hour to two hours over this, so let this be a reminder to make sure you have good backups before flashing. I was lucky I only lost 2.5 months of changes, and that was easily fixed, but losing ALL your data because you don’t have a backup is never fun (I’ve been there)