Blizzard have posted an update on the current status of the Diablo 4 Open Beta and the issues its facing.
Queues and Disconnects (Source)
Hi everyone
Just wanted to provide an update regarding the queues players are experiencing this morning. The team is working through some issues behind the scenes that have been affecting players and causing them to be disconnected from the servers. For the time being, we are managing the rate of players entering the game until we have a full fix for the disconnection issues. This is done so we can ensure stability amongst players who get into the game after the queue process. If you are in queue, we ask that you stay in queue to ensure you do not reset your timer. We plan to have more accurate queue countdowns in place for Open Beta next weekend as noted in our Known Issues post.
We are actively working on these issues for this weekend. Once these are resolved we will be able to increase the influx of players and queue times will be significantly reduced.
We will be updating this thread once we have additional information.