My experience was that I commented from on the mobile site, but felt I needed more time to properly articulate an answer. When I found the time, the comment (perhaps better worded than my answer) had been deleted, and even the OP's response in my inbox was gone, so I had to check the history on another device to find the question.
As the moderator who deleted your comment, allow me to explain.
The stated purposes of comments on Stack Exchange are:
- Request clarification from the author;
- Leave constructive criticism that guides the author in improving the post;
- Add relevant but minor or transient information to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).
That's it. On Mi Yodeya, a fourth purpose is widely in use: to provide a pointer to a possible answer. Moreover, note that in all those cases comments are (quoting from that same page)
temporary "Post-It" notes
— by design, they're ephemeral and can be deleted at any time. I'd go so far as to say that the burden of proof, so to speak, is on those who want to keep a comment (to demonstrate that it should be kept) rather than on those who want to delete it (to demonstrate that it should be deleted).
In this case, the comment met the fourth purpose I mentioned above: it pointed to a possible answer without fleshing it out. It provided a citation to some commentaries and a synopsis of what they said, that helps to answer the question. That's wonderful: it provided the asker with a pointer to where he can get an answer, and it provided potential answer-post authors material to flesh out. Thanks for leaving the comment. But once I saw that an answerer had taken that citation and run with it, posting a full answer that includes the same material, there was no need for the comment any longer, so I deleted it.
Perhaps, at the very least, if a moderator is deleting some of my content, I should be informed of that fact with an inbox message.
Perhaps so. Someone requested that, and I encourage you to upvote the request if you agree with it. See also a related feature request.