The icons that 1Password downloads for your items are stored in C:\Users\Your-Username not directly in your vault. 1Password does this to keep the size of your vault as small as possible, because they’re optional and can be downloaded again at any time.
Check your preferences
Open 1Password and unlock it, then choose Preferences and click Advanced. Disable Tune 1Password for max performance so 1Password can display Rich Icons.
If you used a system-cleaning app
If you uses any sort of software that “cleans up” your PC, it’s possible that it removed the icons from this folder. To download them again, open and unlock 1Password, then choose File > Download Icons.
If you sync with a Mac
If you sync with 1Password for Mac, it’s possible that you used a standard Mac ICNS icon with the .icns filename extension. They don’t work in 1Password for Windows. Instead, use a PNG or JPG file.