I used Tower (3.5.1) to sign into my Bitbucket account and make some change to another repo. Went back to XCode (11.2 beta) on macOS (10.14.6) to push changes for a second repo and started to get "Authentication failed because the credentials were rejected".
The sheet shows the address starting with "https://x-token-auth@bitbucket.org/", a Login popup menu with "Username and Password" (or "Add Bitbucket Cloud account"), a User Name field disabled and set to x-token-auth, and a Password field. I fill in the password I just used with Tower, but it fails still.
Adding a Bitbucket Cloud account is a mystery. It prompts for an Account and Password, but whether I use my email address or username, and that password, it still fails.
Sourcetree fails like XCode does. Tower still works, lucky son-of-a. So I'm not dead. What did Tower do to shut out Sourcetree and XCode? I used OAuth authentication in Tower, not Basic Auth.