Blizzard has announced that transfers from the 20th Anniversary Hardcore servers to PvE servers are temporarily disabled. There is currently an issue with this transfer service, and Blizzard will announce when the problem has been resolved.
We’ve disabled all transfers from Classic Hardcore realms to other intended destinations, so that we can investigate and fix an issue with the service.
We do not yet know when the fix will be complete, and we will update this thread as necessary.