Guitar Lessons in GarageBand not downloadable

Recently, I had to reinstall my iMac. After downloading GarageBand 10.4.11 from the App Store, I also wanted to install the guitar and piano lessons that Apple offers for free.

The piano lessons were working fine, but I had issues with some of the guitar lessons, e.g. with the Basics, lessons 2 (Chords - G,C) and 3 (Chords - A,D). The download was stuck at 0 of 0 KByte and I got the following error message: "GarageBand was not able to install the new sounds. Close and re-open GarageBand to download and install them again."

Well, I did that but it did not help. I also deleted GarageBand and reinstalled it from the App Store, booted my Mac in safe mode, verified the hard disk etc. Basically, I did all the usual stuff that any Apple support agent would ask you to do - to no avail.

Luckily, I have backups of the lessons that I can copy to the GarageBand library folder. Nevertheless, there seems to be something wrong with lesson files on Apple's servers and they should fix it.