It’s not uncommon that the Update from External Review ends in error. This will happen if the review document was handled in Word 2003 or previous versions (even if the .docx format is retained), but it can happen for other reasons as well. However, this is often a solution:

1. Open the problematic reviewed document in any version of Word and accept the changes as desired (if you haven’t already).
2. Copy the thus changed reviewed target column.
3. Insert the copy into the original review document and, as applicable, delete the extra right-hand column or accept all changes.
4. Save the amended original review document and use that for the update process as above.