This is expected behavior. From a discussion on the pytroll Slack channel:
The all_composite_names and all_dataset_names methods use the Readers to decide what is possible (what is loadable/exists). After you resample, the new Scene object no longer has access to the readers so it can't decide what is possible.
if you want to know what is already loaded/created then you should look at list(resampled_scn.keys())
This is expected behavior. From a discussion on the pytroll Slack channel:
https://pytroll.slack.com/archives/C0LNH7LMB/p1616079302072400