Fascinating, I am seeing this exact same issue with SSH keys. When using ssh-add these keys will load into the agent without a problem, but I cannot import them into Seahorse. The files have been generated with OpenSSH, but their file names aren't following the standard id_<algo> and id_<algo>.pub pattern ...
I also followed the advice from that AskUbuntu answer to generate accompanying .pub files, but that didn't work either.
Seahorse also outright refused to import the id_ed25519, whereas the id_rsa worked previously. This seems at least inconsistent.
Fascinating, I am seeing this exact same issue with SSH keys. When using ssh-add these keys will load into the agent without a problem, but I cannot import them into Seahorse. The files have been generated with OpenSSH, but their file names aren't following the standard id_<algo> and id_<algo>.pub pattern ...
I also followed the advice from that AskUbuntu answer to generate accompanying .pub files, but that didn't work either.
Seahorse also outright refused to import the id_ed25519, whereas the id_rsa worked previously. This seems at least inconsistent.
Package versions:
gnome-keyring 3.28.0. 2-1ubuntu1. 18.04.1
seahorse 3.20.0-5