More information please.
What version of InDesign? What type of EPUB are you exporting to?
Reflowable or fixed layout?
My version of InDesign is 2015.3 release, 22.214.171.124 x 64 build.
When exporting, I am choosing the Reflowable option, because I assume it allows the pages to keep going when you scroll.
And I am exporting to the version 3.0 of ePub.
Producing reflowable ePubs is not intuitive. There are excellent online video tutorials on TrainSimple.com and Lynda.com
By the way, I happened to see your post from about a year ago, where you recommended this training video from Lynda.com:
Hi Derek, thanks again!
Also, I was able to use your advice from last year's post, https://forums.adobe.com/message/7331335#7331335, where you explained,
"Briefly, you need to start with the InDesign document, use Paragraph and Character Styles to format the text, anchor any images, understand that no master page elements will be included, create external and internal TOCs. Then you Export it as a Reflowable text ePub."
Based on that, I took a few minutes to learn how to apply InDesign's Paragraph and Character Styles to my simple document. Now, my ePub looks more like what I had intended.
I am looking forward to the detailed video at Lynda.com, as well.
Thanks. It's good to know this type of validator tool is available.