Okay, so after searching the forum without finding answers and going through all the trouble of posting, I came across this post which somehow wasn’t one of the suggested similar posts.
Yaghnob Project isn’t autopopulating because collection projects can’t autopopulate.
And as for why observations aren’t automatically being added to the project, it appears the 25km radius for images is the problem. The help article that’s linked to in that post simply says, “Note that observations with a large accuracy circle, or with a geoprivacy of Obscured or Private, may not appear in small Places.”
So my followup question is: what is the maximum radius of accuracy circle required to allow an observation to be automatically added to a collection project?