Business channel (private app distribution) email invite links are not working

There seems to be a problem adding individual users to a release channel (in our case a private app Business channel). The email is received by the invitee but the link goes to an error page. "WHOOPS! This page is not available right now. Please try again later."

I don't know if this is only occurring with Private Apps or if it's a more general problem. Is anyone else having this issue? Does anyone have a workaround?