I couldn't get the Mahjong trick to work :-(
However, I have Solitaire installed on my iPhone but, in the past, have never bothered to log in on there.
I opened Solitaire on my phone just now and logged in. I then tried to open on my PC and, surprisingly, it worked straight away. I've no idea of the logic behind that, but at least I'm in for now! Will see what happens when I restart later ......