I have had a few reports recently of people not being able to click the accept/decline buttons in the Scheduling Confirmation Emails. The way I understand it is there are so many different options with email clients that it may not work on every one of them. I know I have seen in the past where organizations would put a text link under the button. Of course, if this is a bug I'm experiencing and it should be doing an alternative based on the client just comment below and I'll create a github for it.
Below is an example of what could be.