Deleting the icon cache manually may not work unless the things using it are shutdown at the same time. You'd also probably need to delete the thumbnail cache not the icon one.
Try this, which should delete both the system icon and thumbnail caches, and restarts Explorer and Opus for you: Clear Icon Cache
There's also an Opus-specific thumbnail cache which you can clear under Preferences / File Display Modes / Thumbnails, but it would not normally be used for thumbnails which came via the shell.