Having the exact same issues as everyone mentioned above. Agents going haywire putting lots of stress on the cpu.
I have found a way around it that involves using a windows machine. Simply downloaded the game files and transferred to mac using a usb. I only copied the DATA folder and then hit scan and repair on the battle.net launcher. Game updated and everything works fine.
If you are desperate and dont have a windows machine lying around you can maybe pop into your local tech store and use one of their machines for example. Hope this helps.