If you have access to your database you can run the following query. I had run into a similar issue a while back.
UPDATE wp_posts SET post_name = REPLACE(post_name, '---', '-')
This will bulk replace every ‘—‘ with a single ‘-‘ in the post_name. It may also be wise to run the same command on the ‘guid’ field.
Perhaps someone has a better solution, but this worked for me in the past.