I just got an error message that I've never seen before (not this particular wording, anyway). Unfortunately I wasn't thinking straight so I didn't get a screen shot but I believe the error message said "Not enough currency keys."
I was trying to spend some keys at the time and got that message and (as is unfortunately all too common) there was no button to hit to close the message so I had to close the entire game. When I restarted, the keys were no longer in my inventory but there were no additional troops in my inventory either as far as I could tell so it appears I just lost them.
It was only 8 gold keys so I'm not concerned enough to submit a support ticket or anything but still wanted to share the error message since I've never seen it before in case it's related to the server migration or something.