Yay, found the issue – I was still using PHP 5.4
Updated to 5.6 and all is working 🙂
woo hoo I found links for previous versions, plugin working again. I’m sure it’s plugin interaction, the site is pretty plugin-heavy (18 active plugins). I’d deactivated what I thought were the 6 most likely suspects but no luck. As I test on dev site I’ll post here if I find the incompatibility.
