Thank you for your reports and sharing what’s worked for some of you. Our team is actively looking into these issues and we’ll provide updates when available.
In the mean time, I wanted to share some possible workarounds for the issue that some of you shared already. Some of these may not work for everyone, but please feel free to give them a try!
- Try switching to and launching in 32-bit mode.
- On the Blizzard Application, go to Diablo III.
- Click on Option
, then go to Game Settings . - Scroll down to Diablo III and check “Launch 32-bit client”
- Retest Diablo III.
- Change the game region and switch back.
- Turning off and on the Windows Firewall.
- Manually logging in. Launch through the Blizzard Application, cancel the login and manually enter in the email and password for the account. This may take a few tries, if you have issues, try again about 4-5 times.
This is not a fix, but possibly a workaround until we have more information to share with you all on the issue. Hopefully, one of these options help! If there is something that worked for you, that isn’t listed here, please feel free to share! I’ll try and keep this list updated as well 
Thanks again, everyone!