Based on your description, I understand that some users do not show up in the list after being added to the DL.
According to my tests, when I send an email, the list shows all the members.
Can you provide more information to help me better understand this issue?
1.In the EAC, check if the user mailbox is enabled for "Hide from global address list (GAL) ". If YES is displayed, turn it off.
2.In the EAC, are the new users added shown in the DL?
3.Do all users on the list receive emails?
4.Whether it is all the new users who are added will encounter such a problem?
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.