Probably what happened was somebody deleted a comment: if someone leaves a comment in your LJ and then deletes it, the "comments received" counter doesn't go down. (It's also a very lazy-increment job, both here and on LJ; lazy-increment means there's a chance it may have just missed counting one and may update later when it gets around to it.) Generally, as long as the comments received counts are within a couple dozen of each other, it's pretty likely it got everything. I think the discrepancy when I imported my account was something like 19 comments on like 8 years' worth of entries?

For the community -- go ahead and keep trying, but I've also passed it along to Mark and Robby so one of them can look into it a bit and see if they can figure out what's up. If we wind up having to run it in Super Secret Admin Debug Mode you may receive unexpected success/failure messages in your inbox later and go "wait, what, I didn't start that import", don't worry, it was just us.