This happens when the person who sent you the link to the proof didn’t actually “share” the proof with you ie they “send an email” instead of “share the proof” (the actual words are different I can’t remember exactly the phrase). Therefore you are not recognized as an authorized viewer of the proof when you click the link from the email notification.. You should be able to navigate to the proof if you know which project it’s in and see it that way. I always take this opportunity to send screenshots to the person who sent the link and tell them to always share first and if they have to send the proof again to someone where it’s already been shared, then you can send an email link. It’s confusing this cloud stuff.
One more thing, if you still get to the login page after getting a properly shared link, clear your cache and try again.
