Users missing in Engage

[ArneDD]

Hi everyone,
I am just starting to try out Engage.
I have around 1700 Users in my tenant but in the All Company Group there are only 270 Users.
Also when I try to add users to a group in Engage or write a private message in Engage, I can only find a few users.
I have multiple domains in my tenant, there are some users with a private E-mail adress as Guest, there are many of User type Guest but are internal (so with a UPN under one of my domains) and others of User type Member with different licenses. Be
However I was not able to find a pattern of who shows up in Engage and who doesnt. It seems completely random.
Do you have any hypothesis or suggestions on how to find out why? 

[#2]

Are those additional users licensed for Viva Engage/Yammer?

[#3]

@KevinCrossman as far as I understand,  Members need a license that includes Viva Engage but Guests don't. All Members do have a Viva Engage license. And as I mentioned, I don't see a pattern. There are some Members with different licenses visible and others with the same licenses are missing, and some Guests are visible and others are not. 

[#4]

Sounds complicated and suggest you contact Microsoft Support.