Checkboxes disappearing when opening form

I have created an interactive form in Adobe InDesign CS6 and have exported it as an interactive .pdf form. There are several checkboxes on the page, and for some reason two of them keep disappearing upon opening the form in Acrobat X. I've checked their settings against the other ones that are showing up, and they seem to be set up the exact same way, so I'm baffled as to why they are disappearing.

I've uploaded a couple screenshots—the first shows my InDesign file and the checkbox settings, the second shows how these two checkboxes just don't appear in the file. 

One thing to note: I have inserted this .pdf file into another .pdf file; when opening the .pdf on its own, these two fields sometimes appear, and sometimes disappear.