I can't send you the data. I think I would break several laws if I would do that at this point
Also I don't know how important that work is. I mean my production database is already on 1.9.2 since I migrated directly to that version from the old forum (phpbb2). So this really doesn't affect me at all. I just wanted to report it, perhaps try to understand it and learn something from it. Especially since my knowledge of MongoDB is still quite limited.
This error is happening on an earlier test migration to 1.8.2 that I have still around. So in theory I could just throw it away. Especially if you have no other reports with this problem.
I'll gladly try it with smaller batch sizes. But I kind of doubt that this will make a lot of difference. I have a batch process in my modified solr plugin but with a batch size of 1000 and it is working fine there (Yes, I'll work on the pull requests for solr, I know they are still open ).