I googled it and found this: https://www.tenforums.com/customization/131381-folder-icons-i-customize-keep-reverting-back-default.html
This google -> https://www.google.com/search?q=windows+10+custom+folders+revert&gl=US has some ideas to try but as this is crossposted I'm stopping here.
Like it says on the title. The only thing I can add to that, this is happening on internal HDD that is other than my OS drive.
I customized icons but after reboot, they keep reverting back to default. For years this was not an issue and all of a sudden it is...