Why Sveltekit turn my normal json to flat version

Question

my question is :
in svelte actions, base on document(https://kit.svelte.dev/docs/form-actions#anatomy-of-an-action) when return some json data we can easily access it in client side, but when i try this i faced with a flated version of my json!
for better undrastaning i explain my question with this examples:
Simplified version of the server :

export const actions = {
    search: async ({ request }) => {
        const users = await prisma.users.findMany();
        return {
            data: users
        };
    },
};

and Simplified version of the client is :

<script>
    export let data;
    const onSearch = async (evt) => {
        const response = await fetch('/users?/search', {
            method: 'POST',
        });

        if (response.ok) {
            const newData = await response.json();
            console.log('newData', newData);
        }
    };
</script>

when i console.log(users) on server result is :

[ { id: 1 }, { id: 2 } ]

an when i console newData in my client, i recived this flated data that hard to read and hard to pars:

{type: 'success', status: 200, data: '[{"data":1},[2,4],{"id":3},1,{"id":5},2]'}

where i do wrong that make this happen to me.

p.s:
"svelte": "^3.54.0",
"@sveltejs/kit": "^1.0.0",