Cross references corrupted when using mif

Hi,

I have a FM book that has been updated to FM 2017 ( I assume the client created the files with FM 10 or even earlier). When updating all files within the book all cross references are ok (they are within a book file but also from one file to another). As soon as  I change to .mif and back to .fm, all cross links in some of the files are corrupted (and there are  thousands, it is a 200 page service manual). We need to use .mif for translation, but haven't even started yet as we have the problem already when changing from .fm to .mif back to .fm with the original files. Help!