In my PC there are multiple user accounts. One of these accounts installed Battle.net and Diablo III clients. The other just logged into their respective blizzard accounts and ran the game. The problem is that only the account that performed the installation is able to see the seasonal achievements. The other account see a blank window.
I tracked down the issue and found out that a sub-folder inside the main cache directory is created with special permissions for the primary user only. Even though all the users belong to the administrators group and have rights, they don’t seem to have permission in this specific folder.
To resolve this issue, open the C:\ProgramData\Blizzard Entertainment\Battle.net folder. Right click the Cache folder and assign each user full control permissions. Inside the Cache folder, repeat the same for each subfolder.