same thing just happened to me. After the third phase the cut screen appeared. Then when it was finished the screen went black and stayed that way with the back ground noise still running. I went out and in the game several times. Same situation occurred. Don’t want to quit out cause I used 16 team revives.
It is a known bug with a very unfortunate work around. If you quit and go in with a different champ, then it'll go back to normal. So the options are to wait for a fix (who knows when that will be) or potentially spend an extra revive when or if the bug occurs.