I am wondering what event exactly would cause these auto posts to be created, and where should I look for the source of this?
I guess you have imported many solutions/customization in your CRM, However, here is a work around:
Go to settings>>Customizations>>Customize the system>>SDK Messages
You will see that there are multiple auto-posts plugins enabled for same event on same entity, disable them & let only one enabled:
Make sure to Vote as Helpful and Mark As Answer ,if you get answer of your question.
Do not forget to click on Publish button after that
Thank you for this response earlier... however, I am wondering why only the ActivityFeeds plugin SDK messages are duplicated on a default solution import. For example, we have a third-party plugin library as well as our own, yet these associated SDK messages are not duplicated. What do you recommend to handle this situation?