I noticed a while ago that some of my completed emails were not available in automation. However, I just discovered it is only emails that used Split Testing in their subject lines that are not populating.
Hi there -- What you're seeing here is expected behavior. Split test mailings aren't currently available for use in automated mailings, as mentioned here in our Resource Center. If you're trying to build a link click trigger workflow, you can choose from any mailing that meets the criteria listed at the bottom of that article (not a split test, does not have Google Analytics applied, scheduled or sent to at least 2 recipients).
We do hope to support split test mailings in automation soon!