Client side browser Dev tools log showed that the IIS Server is returning HTTP 404 (Not found) errors.
We also noticed that the actual icon files were present on the storefront server and with the help of Procmon we were able to confirm that the W3Wp process was able to read them successfully.
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IIS hardening has blocked .svg file formats at the IIS server level.
Explicitly allowing .svg file format (because all the missing icons had this format) at the Storefront site level in IIS Console will resolve the problem. To add a specific file format, follow the steps below:
1. On the Storefront server, open IIS console.
2. Browse to the Specific Site that is experiencing the issue.
3. In the middle pane, select Request Filtering option
4. In the File Name Extensions tab, from the Actions menu, Select Allow File Name Extension , type .svg and click OK. Make sure that the extension is added and set to True in the Allowed Column.
5. Close IIS console and run iisreset command from the administrator command prompt.
6. Repeat the steps on all the Storefront servers.
After implementing IIS Hardening settings, icons for Home, Apps and Desktops are missing in the Home page of Storefront where we see the enumerated apps and desktops. In addition, the star symbol for the Favorites are also missing. However users are able to add applications to favorites by clicking the top left corner of the apps or desktops.
For more information on Request Filtering, refer to
https://learn.microsoft.com/en-us/iis/configuration/system.webserver/security/requestfiltering/