NAT Gateway w/ Elastic IP in Public + Private VPC with AWS Workspaces ..

Hi -

We've just setup a NAT gateway to securely provide outbound internet to our Private VPC containing a whole bunch of AWS Workspaces (Windows + Linux). According to the solution we followed, all machines should show the same IP when egressing the network via the NAT gateway. But, that's not happening for us somehow.

Although most machines show the same elastic IP we've configured on the NAT gateway, some are still showing different IPs. How come?

Can someone please help explain this and suggest where we may have made a mistake.