Signin throws an occasional not valid JSON error

signin: async ({ request, cookies }) => {
        let form = await request.formData();
        let email = form.get('email') as string;
        let password = form.get('password') as string;

        try {
            let res = await auth.api.signInEmail({
                body: {
                    email,
                    password
                },
                asResponse: true
            });

            function getCookieValue(cookieString: string) {
                const match = cookieString.match(/better-auth\.session_token=([^;]+)/);
                return match ? decodeURIComponent(match[1]) : '';
            }

            cookies.set('better-auth.session_token', getCookieValue(res.headers.getSetCookie()[0]), {
                path: '/',
                httpOnly: true,
                maxAge: 604800,
                sameSite: 'lax'
            });
        } catch (err) {
            if (err instanceof APIError) {
                return fail(400, { errMessage: err.body.message as string });
            }
        }

        redirect(303, '/profile');
    }