The DevExp team shares the following information:
You're seeing a different schema because runtime GraphQL requests directly to Prismic’s GraphQL API using Apollo Client aren't the same API as Gatsby’s GraphQL API.
<StaticQuery> queries Gatsby’s API at build time, instead of at runtime. The Gatsby GraphQL API does not exist at runtime, so if runtime querying is absolutely necessary, then you'll need to send the queries to the Prismic API.