I belong to the Facebook group, Family Tree Maker® Users where they offer a wonderful Guides section.
Guide 14.08 How to Find All [unknown spouse} is very helpful for cleaning up your tree or just to give you a research project, finding the spouses of these people.
To find all the [unknown spouse]'s in your tree, you need to run the marriage report under the Publish feature of FTM.
You will find the marriage report under the Relationship Reports category.
You will need to run it for "All Individuals" and you actually need to run it twice. Once with "Sort by wife" unchecked and again with "sort by wife" checked. The first report will be sorted by the husband's names and at the end of the report you will have extra wives listed with no corresponding male. The second report will be sorted by the wife's names and at the end of the report you will extra husband's listed with no corresponding female.
NOTE: both reports will print the Husband's name in the first column and the wife's name in the second column.
When I ran these reports for my tree, I had fewer husbands with no wives and I decided to start there.
I searched for the person's name and I excepted to find a man who had children and no wife listed. However, I found a single male, with no wife and no apparent marriage fact.
I decided to switch from the Tree view to the Person view and here I could clearly see there were "shared facts with [unknown spouse]. However, there wasn't any shared facts underneath this heading.
Then I deleted this newly created spouse, by right clicking on the person and selecting "Delete Person". At the popup box, I press [YES] to delete this person from my tree.
Of the 14 males on this list, only two actually had children and thus I had to repeat this process for a total of 12 times. Why this happened, I am perplexed. I do all my data entry in FTM, I don't merge records from Ancestry to my tree. I do sync from FTM to Ancestry. I have been using FTM since version 3 and perhaps during one of the many upgrades over the years, created this situation. It is anyone's guess.
I did find the same situation with my females list. However, not as many in my first dozen names, I only had three. I do have 53 names on my list, so this may take me a little time to get through.
Moral of the story, running these types of reports is a great way to keep our trees clean and from strange situations from creeping into them.
Remember to have fun and Just Do Genealogy!