Internal server error: parent deleted

This error is returned by VK when you try to reply to a comment on a deleted post.
The point is that when a post is deleted in VK (by a moderator or by the user), there is no technical way to find out about it, because. VK does not transmit this data.
Therefore, comments from such posts may remain in the service, but when you try to reply to them, this error is returned.

You may select all comments to such a post (either through theStatistics - Postssection or through the "View comments on the post" link inside the comment window) and close them or delete them manually in the service.