Here is a long thread from almost 3 years ago with an identical issue and how it was resolved.
I’ll spare the paragraph rant but suffice to say, yes, it is Blizzard’s responsibility because it’s locked behind their live service.
Starcraft II Backend Service is the cause
Also, get rid of online authenticator for campaign/singleplayer gameplay. 14 years later. One of the campaigns is free-to-play anyways, right? 100% absurd.