New router download speed way slower than my optical fiber router's

[ChevyW.]

Hello!

 

I'm having a problem and I can't find any old topics that'd help. My PC was connected straight to a fiber optical router (Halny HL-4GMV4) via cable and I recieved 40-50MB/s of download speed (which is what the internet provider is promising) and all was well.

Then I moved to another room in my house. An old router was connected here already through the attic (via cable of course) but I knew it'd be too slow so I changed it to something newer (TP-LINK Archer C6) which promised 1GB/s download speeds but all I'm getting is... 10MB/s download speed now once I connected it to my PC. As far as I'm aware (if my provider would provide me that much speed) I could even be getting up to 100MB/s in theory. 10MB/s isn't bad, it's just less than I expected.

The cable connection goes from the LAN port of my Fiber Router straight into the WAN port of my new router. Then from the new router to my PC.

 

My question is: Where did I mess up for my internet speed to be lowered like this? Is this a connection issue/router setting issue or maybe I got something else than promised?
I'd appreciate any help you could give me.

A (hopefully) helpful diagram is located below for y'all.

[Skipple]

I'm confused, why do you have 2 routers? Are you double NATed?

[FloRolf]

Some routers have a "Eco mode" that throttles the 1gbit port to 100mb like it is the year 2000. Make sure all ports are actually running at gigabit. 

[Sjaakie]

Indeed a strange setup, you'd expect the tp-link router to be a switch.

[ChevyW.]

46 minutes ago, Skipple said:

I'm confused, why do you have 2 routers? Are you double NATed?

Well, I have a big house and we told that to the internet provider so they said: we'll just add another router for you. And they did. Half of the house was covered by Wifi_Named_1 and the other half by Wifi_Named_2

I've no idea why they did it this way, I just re-created it (by swapping a router for a modern one) and noticed a problem with the cable speeds.

Say I was to fix this: how would I go about it?

 

[ChevyW.]

24 minutes ago, Sjaakie said:

Indeed a strange setup, you'd expect the tp-link router to be a switch.

I've read about this too but this is how the provider made it for us when we said one router isn't enough to cover the entire house (WiFi). How would I go about making this router into a switch? Would it fix the speeds?

[ChevyW.]

Hi!
I bought a switch, turned off the DHCP in both the second router and the switch. Nothing seemed to yeld a result so my supicions arose about the cable. Turns out it was some cheap-made one delivered by the ISP company so I asked my friend to lent me his brand new one. After doing that, my internet speed went back to normal. So, I didn't really have to turn off anything or configure anything (even though I did) as it was a faulty cable. I went up into the cold attic to look and saw someone severed it a bit, probably on accident.
Have a good day, guys!