The suggestions provided by @MarshallA are very good things to check for as they can cause a vendor to be classified as under the threshold. I wanted to take a quick moment to include an article that contains steps to resolve issues with this form: 1099 Troubleshooting. Additionally, the article has a section entitled 1099 reports show a lower amount than you've calculated which I recommend looking at.
I'm here if you should have any questions. Best wishes.