Recently I noticed twice that my comments under answers (answer 1 and answer 2) were gone several days after they were posted. In answer 2, only part of the comments, which I actually referred to in my answer, were lost. Is it a system bug or is it deleted according to forum rules?
I deleted the comments in questions. Most of them fell under the "obsolete" removal clause. In addition some not so productive discussion was removed.
This FAQ has some more information on how comments work and who can delete comments.
If I accidentally removed too much don't hesitate to comment the same again (unless a diamond moderator tells you otherwise).
Comments are third-rate citizens on the Stack Exchange network. They can be deleted almost at-will. Please see the MSE FAQ on how comments work.
This is not unique to Code Review. It works like this everywhere on the network.