Viewed on acrobat pdf or others pdf viewers?
There's a couple of things you can check.
In your InDesign document, when you go to a page containing buttons:
Can you see the buttons? If they have disappeared, than they might be set to be non-printing objects.
The buttons can also be placed on a non-printing layer:
Which PDF export settings are using?
If you are choosing File > Export and selecting format Adobe PDF (Print), and Interactive Elements are set to Do Not Include, all interactive objects will vanish from the PDF output.
Instead choose File > Export, and select format Adobe PDF (Interactive)
In the Export to Interactive PDF dialog ensure Forms & Media is set to Include All.