Had the same problem with adding new versions of an app. Just turned out that i was logged in with a user account used for testing, without rights to add a new version. Logout and login again with the right user fixed the problem for me. PS I could also navigate to the test flight screen but then when adding a newer build, it just failed. Again, if i logged out and in it fixed it.
Plus (+) icon is not visible if you already selected build and you just half process got done. in that case you just edit your existing in-progress pending process:
Steps to done it:
-> go to apps
-> click on existing application which you want to upload new version
-> select last version
example:
iOS App
1.3.4 Waiting for Review <----------
1.2.6 Ready for Sale
-> do here what you want like cancel for
-You can edit some information while your version is waiting for review. To submit a new build, you must remove this version from review.
-remove old build file and select new one
that's it.
