This error is generally triggered by our GraphQL Service 

Realm's GraphQL Service works by querying cached Realm files from the server. While these cached files should always be available, there are a few rare conditions where they may get closed. In this event, you'll want to reach out to our support team.  When you do this please provide the following: instance information (i.e. cloud URL or self-hosting version information for all packages) and a reproduction case.