Issue:
On the Profile tab > Collection > Plans, I can see that I am following multiple plans. However, when I apply the filter Following, not all of them show up.
Resolution:
When you filter by Following, you will only see the plans that you are following and that you are not the author of. Therefore, even though you are following them, they will not appear in the Following section as they are already found under the Authoring section.
Additional Note:
Read more about your profile at Your Profile: The Collection Tab.