Chances are, you will see a greater number of hashtag posts listed on the Instagram or Twitter platforms than in the Feeds module.
If you're running a hashtag campaign, please be aware that Feeds will probably not be able to obtain all of the posts that use your hashtag. There are several reasons why, but these all come down to what is made available via the API of each social network.
Feeds can't obtain a hashtag post if:
There is any sort of privacy setting enabled for the poster's account.
The post hasn't been "indexed" by the social network for that hashtag.
The social network has prevented API access to a post for another reason beyond our control and knowledge.
Because of these factors, you will likely see a discrepancy between what's listed on the network itself, and what appears in the Feeds module.
Feeds is also unable to obtain hashtag posts from before you created your Feeds ID because of limitations by the social networks.