I've just noticed several of my comments are gone and I didn't delete them. I don't comment lightly - it's generally looking for clarification from a question or response, or to point out issues in response. I will delete my own comments once I think the issue is resolved, but many are deleted, presumably by a moderator, while the issue still stands, implying I now no longer take issue with the response. That seems awful cavalier and defeats the "community" spirit.
The comment deletion policy is in Why are site comments being deleted? and is guided by the "When should I comment?" and "When shouldn't I comment?" sections of the help article about the commenting feature.
Those two comments were removed as being no longer constructive — the post author rejected the suggested change, and having no further purpose, the temporary notes were removed.