Just tested on my sandbox and it works for me. Here is the code snippet and trace. Did the problem happen on your sandbox or production? Did you use Webhooks or PubNub?

function subscribe_for_notification(){

    subscription.setEventFilters([

      '/restapi/v1.0/glip/posts',

    ])

    .register()

    .then(function(subscriptionResponse) {

        console.log("Ready to receive incoming notification via PubNub.

    })

    .catch(function(e) {

        console.error(e);

        throw e;

    });

}

#####

LMRC7780:QS_NodeCode_4.0 phong.vu$ node pubnub-notification

Login success

Ready to receive incoming notification via PubNub.

SUBSCRIPTION NOTIFICATION.....

{ id: '4514701316',

  groupId: '589053958',

  type: 'TextMessage',

  text: 'Post something',

  creatorId: '178009004',

  addedPersonIds: null,

  creationTime: '2021-01-07T16:54:03.333Z',

  lastModifiedTime: '2021-01-07T16:54:03.333Z',

  attachments: null,

  activity: null,

  title: null,

  iconUri: null,

  iconEmoji: null,

  mentions: null,

  eventType: 'PostAdded' }