I have got it back - I think maybe the update deleted the image file - is that likely? I had put the image in the active theme directory (circle-media-icons)... where should I have put it?
For info, I used:
Sticker ID: circle_mail
Sticker URL: mailto:[:username]
Sticker Name: email (circle icon)
When I first tried to add it back in, before, I think I was an idiot and just used 'email' as the ID, so ignore the bit about the plugin saying it already exists, sorry! :)
PS LOVE this plugin - particularly, being able to customise the HTML output and add custom networks <3