Random GamerTag change

The free gamertag change happens only if you were given one of the random gamertags when you first create your account. From the looks of things, your gamertag is not a system-generated random name. Perhaps you made your account before Xbox began giving
people random gamertags? As it is a custom name, the only way to change it will be through a paid gamertag change.

Have you contacted support to see if they have any info on what triggered the change?

"in some games it shows LT Rive. In others it doesn’t" how does it show on your dashboard on the console?

Hello, first it's a pleasure to be able to help you today.

My name is welcome to the community.

Hello UnderDog, you did correctly in contact with xbox customer service, unfortunately as this forum is public viewing and unfortunately as independent consultants we do not have access there is some data nor your account.

As you have a service number, try contacting support again via chat and pass the number you have so they can track and tell you the status of your request.

https://support.xbox.com/en-au/contact-us

On Call of Duty or your MSA gamertag?

If you have the same username as someone else, you get a # and 4 numbers at the end.