Unauthenticated error on GraphQL for some ips, credentials: 'include' (SSR)

We have a communication between two services, an API and a client. The client is using NextJS and does partially SSR. the API is using a graphql module.

To authenticate we forward cookies from the client. We do this by passing the credentials: 'include' to a fetch query.

This works for 85% of the cases, however for 15% it doesn't. This only happens on the part where we send graphql requests from the client! (so after SSR)

This is the fetch configuration we're using (using apollo).

import { ApolloClient } from 'apollo-client';

let globalApolloClient: ApolloClient<{}> | null = null;

function initApolloClient(
  initialState: {} = {},
  cookie?: string,
): ApolloClient<{}> {
  if (typeof window === 'undefined') {
    return createApolloClient(initialState, cookie);
  }

  if (!globalApolloClient) {
    globalApolloClient = createApolloClient(initialState);
  }

  return globalApolloClient;
}


import fetch from 'isomorphic-unfetch';

function createApolloClient(
  initialState = {},
  cookie?: string,
): ApolloClient<{}> {
  const headers = cookie ? { cookie } : undefined;

  const httpLink = new HttpLink({
    credentials: 'include',    
    fetch,
    headers,
    uri: OurApiUrl,
  });

  return new ApolloClient({
    cache: new InMemoryCache().restore(initialState),
    link: ApolloLink.from([httpLink]),
    ssrMode: typeof window === 'undefined',
  });
}

The GraphQL context can not be created as our authentication cookie is missing in 15% of the cases. What could be the reason of this?