Like it says on the title. The only thing I can add this is happening on internal HDD that is other than my OS drive. I customize icons but after reboot, they keep reverting back to default. For years this was not an issue and all of a sudden it is...
Can you please list your specs like so:
Include the version of the OS you're on. Make sure you're on the latest BIOS update for your motherboard. On a side note, go into BIOS and see if the HDD you speak of is found in Bootable Devices options.
This seems to be a result of a Windows 10 update, you may want to uninstall the Windows last update and see if the issue persists. If it does, here are couple of things you can try. Right click on your desktop and click on "Refresh" and uncheck auto arrange. Another fix is right click on the desktop and click Personalize, click on Themes and scroll down to Desktop Icon Settings, and uncheck the box that says, "Allow Themes to Change Desktop Icons". Click apply and then back and see if your custom icons are still there after a re-boot. You can also look through this post https://www.tenforums.com/general-support/17175-windows-10-folder-view-settings-desktop-icon-positions-not-saving.html