I had a similar issue where my "Playgrounds" folder on iCloud Drive was corrupted for some reason.
Simple solution:
Go to Settings > Apple ID (your name on top) > iCloud > iCloud Drive > Apps Syncing to iCloud Drive > Toggle Playgrounds off
More complicated solution (if you want it to sync across devices):
Delete Swift Playgrounds from all your devices
In the Files App, go to iCloud Drive and delete the Playgrounds Folder
Reinstall Swift Playgrounds
Topic:
Developer Tools & Services
SubTopic:
Swift Playground
Tags: