Hey again everyone,
Our Battle.net engineers have identified what is causing this issue and are working on pushing a fix out. We do not have a timeframe for that however.
As others mentioned, the best known workaround for this is to uninstall/reinstall WoW through the Battle.net app and then disable downloading of future patch data. You can disable this in the Battle.net app Settings under Game Install/Update -> Automatic updates -> select “Apply latest updates for recently played games”.
This of course is a temporary workaround while the core of the issue is being worked on. Once the issue is resolved you should not have to redownload the game and the fix should patch up your existing install.
If you want to be covered for future patches, we would recommend to go back in and re-enable downloading future patch data after patch 9.0 has released.
Thank you again for all the reports, the logs, and for sharing the workarounds you’ve found.