tl;dr: NEVER use spectating mode while waiting for matchmaking, it will ban you.
I queued in yesterday and was waiting for a match. I decided to spectate in the meantime. I selected a match that wasn't in the first page. I saw a message that it might take a moment for spectating to be started. Immediately after this I completed matchmaking and was placed into a game. After being placed into a real match the spectating mode started and placed me in spectating, causing me to leave my match. I tried to leave spectating, but received a message that I would receive a temporary ban... I had no choice and thought maybe I could "rejoin" match from the main menu, but no luck. I get a 4 hour ban for effectively leaving spectating mode that I didn't want to be in .
Little searching and it looks like this was reported in October and never addressed: https://forums.playdeadlock.com/threads/leaving-spectating-mode-is-prohibited-from-ranked-matches.39855/
I queued in yesterday and was waiting for a match. I decided to spectate in the meantime. I selected a match that wasn't in the first page. I saw a message that it might take a moment for spectating to be started. Immediately after this I completed matchmaking and was placed into a game. After being placed into a real match the spectating mode started and placed me in spectating, causing me to leave my match. I tried to leave spectating, but received a message that I would receive a temporary ban... I had no choice and thought maybe I could "rejoin" match from the main menu, but no luck. I get a 4 hour ban for effectively leaving spectating mode that I didn't want to be in .
Little searching and it looks like this was reported in October and never addressed: https://forums.playdeadlock.com/threads/leaving-spectating-mode-is-prohibited-from-ranked-matches.39855/