After the initial download of 4.0.0, when I first opened I was not prompted to login (I was already logged in, in another instance of Studio 3.X). After having environment issues, reported in other tickets (
TISTUD-7366 & TISTUD-7364) I shutdown studio. When I reopened I was asked to login, then prompted to select my org, then told my login failed (see screen shot). I then re-opened studio and tried again and it worked.