Players cannot connect even though ports are open

This is a really strange problem. All of the relevant ports are open (I opened 27005 - 27500 on both TCP and UDP to be sure). Additionally, while Googling, I found this guide which said this:

so I opened 1200 and 26901 as well but the issues are persisting. Players can sometimes connect but then sometimes can’t. It happens to me too: one minute I can connect to the server, a few minutes later if I DC and try rejoining I will get “connect failed after 6 retries.” It never loses connection while connected.

Here is my port setup:

The server that is running on the default ports is not having these issues. sv_region on all servers is set to 0 and the machine is a dedicated Linux box hosted in some datacenter. I’ve tried Googling for a while but most threads I find on various websites are about port forwarding and people running servers from their house.

If anyone wants to try testing HLSW or any other tool the IP is 149.56.28.95

Hey, just in case anyone finds this on Google in the future:

I ended up contacting my host’s support as the issue was so strange.

They have something called a “GAME firewall” which apparently was activated by default and automatically had a whitelist for 27015. As to why it sometimes allowed traffic on the other game ports and sometimes not, I have no idea (really strange for a firewall IMO). It was also hidden deep inside their control panel. If anyone else finds this issue on Google, I’m using OVH and you have to go the IP’s management tab and then hit the cog all the way on the right and hit configure.