All IOS apps icons suddenly missing in iTunes

Hi,

My iTunes library is located in a USB drive. Today, while I was using iTunes, the drive disconnected, which led to various errors.

Until now, closing iTunes, reconnecting the drive then re-launching iTunes was enough to fix the errors. But today, this doesn't work:

All the IOS apps in the iTunes library are missing their icons!

Only the apps I re-downloaded or updated manually since the issue occured get their icons

How can I get them back?

Many thanks for any help.

Using iTunes 12.5.6.5