Unexpected long response delay on observerChanges

I need some help to solve this issue detailled in this github Using APM trace explorer, observeChanges on collection takes awfully long time · Issue #77 · robfallows/tunguska-reactive-aggregate · GitHub

Checked :

  • apm monitoring
  • indexes are fine
  • direct request returns in ms
  • unblock is set

I’m suspecting :

  • bad connexion/configuration between galaxy servers and atlas mongodb oplog
  • mongodb driver 4.17 with meteor 2.14 needs to be updated

what else ?