Maps in a sidecar will not show clustering. I've got a points layer that I have enabled clustering on in the webmap, but it doesn't show it as clustered in the story map. Map notes won't show up either even when the visibility is toggled on.
Is the web map you have created shared publicly so we can access it to investigate the properties of? Are the map note layers using a custom picture marker symbol for the points/lines/areas? If so, do you know if the server you're requesting it from has CORS enabled on it to allow cross domain requests?
I had restarted the story map a few times to try to get it to work with no luck, but it seems to be working now that I've gone back to send it to you. I was just using one of the default map notes from ArcGIS online and for some reason it wasn't showing up for a little while. Seems to be fine now though. Sorry for the confusion.
The ability to view feature layers with clustering is not available yet but is on the roadmap for the 4.x API.
Thanks for the info Aravind. I always assume you guys are aware of a lot of these issues, but just figured I'd point things out as I encounter them.
Retrieving data ...