DeltaSync-Update function in SubscriptionQuery is never called

I am implementing my own Sync object as I am working with connectionModels. Everything works fine with the BaseQuery and DeltaQuery objects. however when I do a mutation, I expect the update function from the SubscriptionQuery object to be called and then be able to update my queries according the most recent data, however this never happens. the update function is never called. I am working with this client https://github.com/awslabs/aws-mobile-appsync-sdk-js, i tried to debug the code but couldn't find any information.
This is how is my code as referenced on the amplify documentation https://aws-amplify.github.io/docs/js/api#delta-sync & the types detailed in the code https://github.com/awslabs/aws-mobile-appsync-sdk-js/blob/997e3d8a958ee2e2d9ffd00fd1eaf20e11343c98/packages/aws-appsync/src/client.ts#L275

subscriptionQuery: {
   query: gql(onSubscription),
    variables: {
     id:  { "eq": this.id},
    },
    update: (store, {data}) => {
        console.log(data);
        console.log(store);
     }
},

Also I created a standard subscription, to check if the issue was on the backend but no, the subscription worked fine with the following code

this.randomSubscription = await this.client.subscribe({
     query: gql(onSubscription),
     variables: {
      id:  { "eq": this.id},
     },
}).subscribe({
     next: (data) => {
          console.log(data);
      },
      error: error =>{
              console.log('ERROR----->',error)
      }
});

I would really appreciate your feedback on this issue.