Trouble adding a group from a root domain to a newly created user object in a child domain

I have an AD environment with a root and two child domains. I need to add groups that live in the root domain to a newly created user object no matter which domain it’s created in. After creating the object, I check to see if it’s in the global catalog and if not, I sync the object. I then have a function that checks the replication and waits until it’s found. It doesn’t seem to sync in a reasonable amount of time. Can someone give me an idea why?

Function Get-UserReplication {
    Param (
            try {
                $NewUser = get-aduser -Server $Server -Filter {DistinguishedName -eq $DistinguishedName}
                Write-Verbose "Waiting for replication."
                Start-sleep -Seconds 30
    } While (!$NewUser)

    Return $True

# Other stuff that reads a JSON file from PowerAutomate with new employee information and creates the object.
# This works and then I try to wait for it to finish replicating.

# If not in root domain sync new user object to root domain
If ($UserDomain -ne $RootDomain) {
    Get-ADUser -Identity $NewUserObject.samAccountName | Sync-ADObject -Destination $RootDomainGC

    Get-UserReplication -DistinguishedName $NewUserObject.DistinguishedName -Server $GCLookup


# Add user object to licensing groups
$Licenses = $NewUserObject.licenses.Value

foreach ($License in $Licenses) {
    Write-Verbose "Adding new user to $License."
    Add-ADGroupMember -Server $RootDomain -Identity $license -Members $newUserObject