If I'm understanding the issue correctly, we are seeing the same thing: when we have a point feature class in a web map where we do -not- change the symbology from the default symbology published with the feature service, i.e. we are not setting the symbology in the web map layer, then the point features do not show up in Collector v19.0.1. We are using Collector on iOS devices, v11.x and 12.x.
If you set the symbology in the web map then it works around the issue, but this seems like a bug with Collector.