The broadcast data check goes through the broadcast data table and for each row checks:
After finding the problems, you are presented with one or more tables containing a list of the errors. You can then either ignore the errors or choose to repair them selectively.
The above list is repaired in the follow ways:
This means that there are two children that both point to the same parent. Search for the post in the child blog and you should see two posts that are identitical expect for the slug.
Find the slug that ends with -2 and delete that post. Then rerun the check, relink the parent and you should not receive any more unlinked parent errors for that child post.