not sure if you were able to figure this out. But when you access your Admin UI, does it give you any message before allowing to proceed to Admin ui over HTTPS ?
seems like you have a hierarchy of certificates, all of which should be trusted on the client. It's complaining about not finding certification path.
Which means that your client machine might trust your LC server cert, but may not trust parent or intermediate certs.
usually browsers just throw a prompt and let you move, but the launchpad does not have any such prompts, so it errors.