Some nesting mixups here:
looking at https://mastodon.social/users/kevinmarks/
<data class='p-name' value='kevinmarks on mastodon.social'> isn't setting the p-name of the feed, and is wrapping the whole h-feed div in a <data> element, as <data> isn't self-closing.

The non-repost entries don't have class="h-entry" so aren't showing up as entries, but their properties are being put into the h-feed instead:
http://www.unmung.com/mf2?url=https%3A%2F%2Fmastodon.social%2Fusers%2Fkevinmarks%2F&html=&pretty=on

<div class='entry'> should be <div class='entry h-entry'>

The posts look better, though adding u-comment to the h-cite will make them nest better:

https://indieweb.org/comments#How_to_markup