In my first three months, I've had two different companies cancel on me, in both cases without sending a 'sorry but we had to cancel your shop' e-mail. I issued them both a flake citation.
(I didn't tell them about it, but it's there.)
I e-mailed one company to ask them if I'd done anything wrong. They promptly answered, saying that the client had just changed its mind about something. I've done a couple of jobs for them, and more coming up.
I tried to get in contact with the other company, and they had no e-mail access unless I had an assigned shop, which, of course, I didn't. I don't check their job board any more.