Randomly getting Disconnected

Hello.

For a couple of months now I’ve had some disconnection issues. It can happen several times during one hour, then it can run smoothly for a couple of hours then it comes back.

I live in an apartment with Fiber internet, so we have a raycore fiber converter and regular router that we got from out ISP.

At first I thought it was my ISP so I contacted them. After talking to them I got instructed to connect my internet cable directly to the raycore and that solved the issue! I live with my girlfriend that also plays wow with me and she kept getting randomly disconnected meanwhile she was connected to the router and I didn’t.

Note: We tried playing on the Wi-Fi but we kept getting disconnected that way too.

I called back and they sent me a new router. Problem is still there.
I called back and they made an case/ticket for me. Couple days later they message me saying that the problem isn’t within their network.

This gave me an idea, I tested other games and its only wow that we keeps getting disconnected from. Please help us! I want to get rid of this before Shadowlands!

This is what we have tried so far:
Reset router + modem.
Changed Router
Changed ALL internet cables.
Flushed DNS.

Also unchecked the “Optimize Network for Speed” option under the network settings ingame.

Sorry for bad English. I hope it make sense what I wrote.