Recommended Answer
Hi, I found an issue.
First, here is more details:
If machine in the domain network, RD Gateway worked
When machine is in the foreign network, I got this NLA error.
This settings solved the problem:
 - S1M1 (Administrator).png)
Even though I didn't setup my RD Gateway to be specifically a KDC proxy, it seems it is by default (Windows Server 2016) and it works.