Hi @FelipaReyes - I normally see problems converting Word documents to proofs when the file size is too large. Files must be less 4GB is the overall rule, but for Word documents specifically that number is much less at 512MB. If they are over this size, maybe converting the files to PDF for proof would help?
If the files aren't over 512MB then might be worth reaching out to WF Support so they can login directly and see the problems first-hand.