It is possible that you have the key in _two_ keyrings in trusted.gpg.d/ & in trusted.gpg itself.
It would be best for you to do the following:
1) sudo apt remove --purge ubuntu-dbgsym-keyring
2) sudo apt-key del 0xC8CAB6595FDFF622
3) sudo apt-key list | grep C8CAB6595FDFF622 => it should be empty now
4) sudo apt install ubuntu-dbgsym-keyring
It is possible that you have the key in _two_ keyrings in trusted.gpg.d/ & in trusted.gpg itself.
It would be best for you to do the following:
1) sudo apt remove --purge ubuntu- dbgsym- keyring
2) sudo apt-key del 0xC8CAB6595FDFF622
3) sudo apt-key list | grep C8CAB6595FDFF622 => it should be empty now
4) sudo apt install ubuntu- dbgsym- keyring