I temporally got PDF icons working again by changing my default handler of ico file to paint (which still doesn't open these ico files in 10). But after a reboot it was back. I remembered we use Group Policy to set default program handlers in Windows 10 using an XML file. So I altered the XML file to default ICO files to Paint. Now the issue is across multiple computers instead of showing the generic "photos app" icon, it showed the generic "paint" bitmap icon. So I changed it back did gpupdate /force, rebooted and now I'm back to square 1 again.