Get-ADGroupMember : The size limit for this request was exceeded

This is due to a limit with Get-ADGroupMember having a 5k limit, so this is telling you that the group you are trying to get members from has more than 5k Members.

To get around this you can use this

$group = "GroupName"
 $Get-ADGroup $group -Properties Member |
     Select-Object -Expand Member |
     Get-ADUser -Property Name, DisplayName

Myself I ran it as such so I can do a compare with it.

$group = "GroupName"
$Group2 = Get-ADGroup $group -Properties Member |
    Select-Object -Expand Member |
    Get-ADUser -Property Name, DisplayName
$Group2.count