Problems with Master List

[FutureRave]

This question "I don't see my server on the Master List" has been asked so many times and I apologise for that.
But I think I have a different issue than others:
I'm using Google Cloud VM instance feature to create my instance where I intend to host the server.
I followed the tutorial and I am able to start the MW3 server with no problems, or so it seems.
If I type 'status' I get the usual response that a working server would give but it doesn't show up in the master list.
I figured this problem is much more complex than just opening some ports on the firewall.
Does anybody know if this is caused by an improperly VPC setup?
I'm not a super expert on the matter, I tried to read the documentation provided by Google and the 27000-28000 ports are opened for ingress/egress traffic and VM instance is properly tagged for the firewall rules to apply so the ports are not the issue.
It seems that I am missing something else to allow others (Including me) to reach the Instance because even I can't join it if I try to direct connect (nothing happens).
I was wondering if there is a networking expert here who knows how to deal with Google Cloud.

P.S.
I have obtained in the past the 300 euro voucher for Gcloud for free (a signup bonus) so that's why I'm using their services and hopefully I can get this thing running.

Many thanks

Edit:
I don't think I need to create a Cloud NAT because the last thing I want to confuse incoming packets is to use a shared IP. (Or am I wrong?)
So do I need to manually create VPC to decide where the traffic goes?
Edit 2:
I found out a lot of people use OVH as their VPS provider for MW3 Basically one friend of mine sent me a screenshot of his desktop (VPS) and there's is the Google Cloud shell. Basically OVH uses Google cloud to create VMs and then resells you the product. So now I'm 100% sure that there's a way to make a MW3 server using Google cloud (without giving money to a third party). So I would appreciate it very much if someone know how to setup the networking part.

[Mr. Android]

Spectre any clue?

OP - try using this website from your server and see if it can see the ports as open. Also ensure you opened UDP ports and not TCP.
https://www.ipvoid.com/udp-port-scan/

[FutureRave]

Thank you for the quick response, I checked with the tool and basically the ports result open. Specifically, it says Open|filtered with service unknown for the master port and half-life for some other ports I also opened.

[Mr. Android]

I just want to check the basics, can you screenshot your server cmd window for me? So we can see the console output?

[FutureRave]

Of course, keep in mind that I'm running basically the default setup for the server, I basically only removed rust from the map rotation and basically that's it. And for the sake of testing (if I've done something stupid) I disabled WIndows firewall
This is the StartServer.bat

@echo off
.\bin\plutonium-bootstrapper-win32.exe iw5mp "C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Modern Warfare 3" +set key "KEY +set net_port "27017" +start_map_rotate -dedicated 

Log:
https://pastebin.com/ETV9eutu

Edit 1:
Nevermind now I see the server in the list. I wish to know what the **** I've done other than disabling the firewall because this is not the first time I disable everything because the thing doesn't show up lol. I'll post edit so to see if it was Windows Firewall or something else.