I'm not really familiar with the FeedWordPress plugin, but the problem could be caused by the way the plugin creates new posts on your site.
Jetpack tries to catch all post status transitions to "Published", and will share your post if it's not private. But if the FeedWordPress plugin doesn't go through this transition when adding posts to your site, Jetpack won't share the posts.
Did you recently update the FeedWordPress plugin on your site? It seems it wasn't updated in the past few weeks, but that could explain the change on your end.