The MyAccount page uses the OrderHistory service and has a cancel option which is running into a permission issue

Permission Violation: You need the Transactions Sales Order Approval permission to access this page

I did some playing around and this will run if I give it a non Customer Center role with elevated permissions. However, the minimum I can get it to work with is far too much permission to be secure. Is there a way to add the Sales Order Approval permission to a Customer Center role?

So, we did change the behaviour of order cancelling a few months ago and some customers reported problems after we did that. I would probably raise a case and ask if you might be affected by issue 773177 or the follow-up issues.

Will definitely give that a shot.