Have you tried to change the region the game is connecting to, and then changing back to the region you want to play on?
You can change the region by clicking the little globe icon next to the game version dropdown in the Battle.net client.
I’ve also seen some people reporting this when having Razer Synapse installed, is that something you have installed? Or are you maybe running Windows 11? There’s a few different reports I’ve seen that could be causing it, and OneDrive is one of those things, which Windows 11 forces to be enabled.