Writing interaction steps to the cache caused the GET_EDIT_CAMPAIGN_DATA query to be re-fetched.
The results of re-fetch then overwrote the local changes for pending interaction step changes. This
re-fetch happened because in apollo-client@3 cache-and-network fetch policies re-run whenever there
is a cache update that affects the query.

For more information, see:
apollographql/apollo-client#6760 (comment)

Adapts to two apollo client changes:
1. readFragment returns null for insufficient data instead of throwing MissingFieldError exceptions
2. writeFragment now only writes to fields present in the fragment itself