From a Google search it seems this is a common problem.
I have a LiveJournal site with over 1500 posts and 21,000 comments. Importing works fine; all the posts import correctly. The comments import, but often end up attached to incorrect posts.
Comments that are attached to the wrong post are usually erroneously listed as being made by "anonymous." Some of these posts are from people with LiveJournal accounts, some are not. (Some of them are even comments that I have posted!)
Some, but not all, of the comments that come in attached to the wrong posts end up "pending" rather than "approved".
There is no rhyme or reason to the posts that the comments end up getting assigned to; they don't get assigned to posts that are, for example, one or ten or a hundred posts away from the proper post. However, it is always consistent. If I delete the entire database and re-run the import 10 times, all 10 times the same comments will be attached to the wrong posts and they will be attached to the same posts.
Dates, times, and content of the comments always get imported correctly. Post authors, post numbers, and post thread numbers always get imported incorrectly.
There is no relationship between the correct post number of a comment that is imported incorrectly and the comment's thread number (for example, I had thought that perhaps commets were getting assigned, say, to post 80632 if their parent comment number was 80632, but that does not seem to be the case).
I can give specific examples of the data being returned from LiveJournal and the data as WordPress importer sees it. In one example, a comment is coming in from LiveJournal with the following information:
But when the import plugin parses the comments, if I look in $matches in the part of the plugin that examines the XML of the comments, for some reason it's coming back with
Everything else (the comment body and so on) is OK. I don't know if there's a subtle error in the regex (I suck at regex!) or if it's not starting correctly at the header of this particular comment or what. When this comment is imported, it also ends up pending rather than approved.
Like I said, the failures are consistent. This particular comment ALWAYS ends up assigned to jitemid 238112.
Recent comments seem more prone to this problem than older comments. My blog has about 21,000 comments, about 1,000 of which end up attached to the wrong post and pending rather than approved, and another several thousand of which end up approved but still attached to the wrong post.