The network is having a hard time. Signing into your account is one of the things that are affected by the current issues with the Sony Network.
It is not clear how widespread the issues are. I have been able to connect online in Bloodborne and send a message to a colleague, but the PS Store is having trouble loading a lot of content. There are some serious issues connecting online that are shown in this thread on the r/PS5 subreddit.
There are more than 14,000 user reports of issues with the PSN.
The issue has been pointed out by the game company, which pointed out that players of the game may be experiencing login issues. I was able to get into a match even after quitting the game and restarting it, because the problems don't seem to be affecting everyone.
Update April 12th, 7:44PM: Added a post from the game.