Twice now, one in quick play and one in comparative when entering the match from the practice range I have a completely black screen with no hero selection. pressing escape does not even bring up the menu. The only thing I see is the chat log. This seems to only happen from the practice range as all the other work fine.
Are you using Razer Chroma software by any chance?
If so please check this article: Known Technical Support Issues - Updated Dec 8, 2019