I have an application with a combination of user feeds and one curated feed which is posted to by users we pick. All user feeds follow the curated feed. I can see in explorer that the follow relationships are set up and that activities are being posted in the curated feed, but the activities do not show up in the user feeds. What could cause this?
When you add activities using the add to many endpoint client.addToMany(activity, feeds) you are not going to get them propagated to followers.
This endpoint exists mainly to support use-cases where you want to publish the same activity to many feeds but do not want them to propagate via follow relationships (ie. think something like location based notifications).
For your needs you can add one activity to many feeds using the to targeting field:
feed.add_activity({..., to=other_feeds})
Please keep in mind that up to 100 feeds can be specified as targets.