If the ArcGIS Online hosted feature service's source data comes from a featureclass with shapeZ geometry type, then Collector errors out and won't capture the point. I was using Pro to share a shapeZ feature class to ArcGIS Online to use offline in Collector. However, it won't capture the point. I think there needs to be an exception to ignore the Z or place a default 0, in the geometry for Z. The unintended consequences of making it easy for users to "share as web layer" is that not all geometry types are supported in Collector like Z and M. Whereas, in the ArcGIS Online Webmap, you could add additional points, or edit points, without error.
