What are the steps required to reproduce the bug?
Add a defer tag to the script tag of the main js file e.g. with ADVAGG module or via EventSubscriber.
What behavior were you expecting?
No problems with the former domready handler (Drupal 8.7.10). Alle Drupal behaviors were added and executed.
What happened instead?
With Drupal 8.8.1 the attachBehaviors function is executed but the behaviors variable contains an array and not an object which is required for attaching all behaviors in the loop.
---
This is a massive performance issue and should be looked at ASAP.
Fixed
9.5
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.