add minimal reproduction with passing test (upgrade to Ember 3.21.1 f…

…or failure

app/adapters/child.js

@@ -0,0 +1,5 @@
+import RESTAdapter from '@ember-data/adapter/rest';
+
+export default class ChildAdapter extends RESTAdapter {
+
+}

app/adapters/parent.js

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+import RESTAdapter from '@ember-data/adapter/rest';
+
+export default class ParentAdapter extends RESTAdapter {
+
+}

app/components/my-component.hbs

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+<img src={{@src}} {{did-update this.handleUpdateSrc @src}} />

app/components/my-component.js

@@ -0,0 +1,9 @@
+import Component from '@glimmer/component';
+import { action } from '@ember/object';
+
+export default class MyComponent extends Component {
+  @action
+  handleUpdateSrc() {
+    console.log('here');
+  }
+}

app/controllers/application.js

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+import Controller from '@ember/controller';
+import { inject } from '@ember/service';
+
+export default class ApplicationController extends Controller {
+  @inject myService;
+}

app/instance-initializers/preload-store.js

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+export function initialize(appInstance) {
+  const store = appInstance.lookup('service:store');
+  const myService = appInstance.lookup('service:my-service');
+
+  store.pushPayload('parent', {
+    parent: {
+      id: 1,
+      name: 'Parent 1',
+      avatarURL: 'parent.jpg',
+      child: 1
+    }
+  });
+
+  store.pushPayload('child', {
+    child: {
+      id: 1,
+      name: 'Child 1',
+      avatarURL: 'child.jpg'
+    }
+  });
+
+  myService.parent = store.peekRecord('parent', 1);
+}
+
+export default {
+  initialize
+};

app/models/child.js

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+import Model, { attr, belongsTo } from '@ember-data/model';
+
+export default class ChildModel extends Model {
+  @attr() name;
+  @attr() avatarURL;
+
+  @belongsTo('parent', { async: false, inverse: 'child' }) parent;
+}

app/models/parent.js

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+import Model, { attr, belongsTo } from '@ember-data/model';
+
+export default class ParentModel extends Model {
+  @attr() name;
+  @attr() avatarURL;
+
+  @belongsTo('child', { async: false }) child;
+}

app/routes/application.js

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+import Route from '@ember/routing/route';
+import { inject } from '@ember/service';
+
+export default class ApplicationRoute extends Route {
+  @inject store;
+}

app/serializers/child.js

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+import RESTSerializer from '@ember-data/serializer/rest';
+
+export default class ChildSerializer extends RESTSerializer {
+
+}

app/serializers/parent.js

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+import RESTSerializer from '@ember-data/serializer/rest';
+
+export default class ParentSerializer extends RESTSerializer {
+
+}

app/services/my-service.js

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+import Service from '@ember/service';
+
+export default class MyServiceService extends Service {
+}

app/templates/application.hbs

@@ -1,5 +1 @@
-{{!-- The following component displays Ember's default welcome message. --}}
-<WelcomePage />
-{{!-- Feel free to remove this! --}}
-
-{{outlet}}
+<MyComponent @src={{this.myService.parent.child.avatarURL}} />