ePub TOC Missing some components

I'm having a terrible time with my TOC. I don't know what is going on or why it is happening but some of my chapters are missing. I create the ePub from a word docx file using calibre. Everything is working perfectly when I view the ePub in iBooks or in the epub viewer. In addition, the file passes ePub check and validation.

However, I'm getting errors from distributors saying that the TOC is incomplete. I went through my TOC and made sure that all of the (untitled) places were corrected. I also made sure all of my chapters and subheadings were included. Then I manually renumbered all of the play orders so they were sequential. Now, I'm still having the same issue.

Is there another place that needs to be changed or updated?

Any help is much appreciated.

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