Emails went out CC and not BCC as expected

Problem/Motivation

Emails are going out CC and not BCC.

This just started happening.

Code in play:

Drupal core 8.9.8
Mail System 8.x-4.3
Admin Content Notification 8.x-3.6
SendGrid Integration 8.x-1.6

Also SendGrig service.

I'm not 100% that sendgrid_integration is the cause of the issue. Not sure how to troubleshoot.

I would appreciate any help in figuring out where the problem lies and how to fix it.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes