It doesn’t matter if it was this week or earlier. The question was if you ever clicked Play before allowing the patching to complete. Doing so corrupts the game files and causes it to attempt to download during the game, which further corrupts the files since CASC doesn’t like being accessed while it’s patching.
If this continues for you, I would suggest deleting the /Data folder inside the WoW folder (while the Battle.net ap is not running), emptying the trash, and launching the Battle.net app and clicking Update (the Play button will have changed to Update due to the BDA detecting missing files). Let the update process finish completely before you click Play.
If nothing else, this eliminates corrupted files as an issue and gives you a fresh contiguous install, which would speed up your loading screens, especially if you’ve got the game installed to an APFS volume, which double dips on CASC’s inefficiencies since APFS shares the enumeration scheme used by CASC.