Loading Screen Stall Bug
Sometime within the last 3 updates there has been, for better way of describing it, a loading screen bug. It makes it so that you get on the loading screen, it gets to 100, the wheel is still spinning and your ping still registers, but it doesn't put you into the game. If you alt-f4 out of that it will briefly put you into the game before exiting, as though it had always been on the cusp of just about to load. Players have reported that they are getting low priority queues because they were waiting for the game to load for them, even though the game has loaded for everyone else, and end up with "the game you are joining is no longer there" type of messages.
I myself have experienced this as well, and from my perspective I saw it happening whenever I was doing something potentially load intensive like watching a youtube video in the background while waiting for it to load, only for it to never load. Whatever change or update happened affected the loading screen such that if it isn't getting 100% focus as its loading it will stall and never load the game despite still being active.