When the config is in a file, (ig/ref ...) doesn't get evaluated in the dependent method- see core.clj below. It works as expected when config is a literal (see core2.clj)

config.edn

{:hello-integrant/data
 {:my-data {:a 1 :b 2}}
 
 :hello-integrant/consumer
 {:id 1
:param (ig/ref :hello-integrant/data)}}

core.clj

(ns hello-integrant.core
  (:require [integrant.core :as ig]))
  
(defmethod ig/init-key :hello-integrant/data [_ {:keys [my-data]}]
    my-data)
    
(defmethod ig/init-key :hello-integrant/consumer [_ {:keys [id param]}]
  (println :ID id :PARAM param)
  param)
  
(def config (ig/read-string (slurp "src/hello_integrant/config.edn")))

(ig/init config)

;; => :ID 1 :PARAM (ig/ref :hello-integrant/data)

core2.clj

(ns hello-integrant.core2
  (:require [integrant.core :as ig]))

(def config {:hello-integrant/data
             {:my-data {:a 1 :b 2}}
             
             :hello-integrant/consumer
             {:id 1
              :param (ig/ref :hello-integrant/data)}})

(defmethod ig/init-key :hello-integrant/data [_ {:keys [my-data]}]
    my-data)
    
(defmethod ig/init-key :hello-integrant/consumer [_ {:keys [id param]}]
  (println :ID id :PARAM param)
  param)
  
(ig/init config)

;; => :ID 1 :PARAM {:a 1, :b 2}