Hi Guys,
I was with the same problem.
I received the invite in the email, but when I clicked in the button, the link didn't sent me to the invitations page.
I discovery that it is caused by a wrong characters in the link. I don't know if it is a Bitbucket/Atlassian issue or is caused by the email provider.
So, to solve you need to get the link for button "Accept my invitation" in your email, started with "https://id.atlassian.com/signup/invite?application=bitbucket..." and replace the following characters as in the image example:
%253A replace to :
%253D replace to =
%25253A replace to :
%25252F replace to /
This characters appears for me, maybe for you there are another one.
After that I was able to put the link in the browser and access the invitation page.
Hemerson Lima.
Good Look