I've been setting up the Instagram business api access and have for the past few days been setting up the webhook for story insights. When I went to go run a test today the section is no longer in my webhook dropdown. The only thing that has changed since yesterday is that we added the Marketing Api.
After doing a bit more research it looks like this is a known issue though it isn't included in the depreciation changelogs. Facebook says they are looking into it https://developers.facebook.com/bugs/553848658320920/.