@David-TP 

Hey, 

Thanks for the quick responses.

My router is Zyxel vmg3925-b10b.

Old setup was fiber optic modem -> zyxel vmg3925 (to distribute rj45 around the house, wifi disabled) -> asus Ac1750 (in living room to distribute wifi). This worked fine with every device, but the wifi coverage was not good enough, and to solve that, I purchased the X55 units.

I now tested the setup so, that I took out the Zyxel and connected X55 to the fiber optic modem. This seems to work with my Samsung S24 for some reason. Now the problem is, that I have the main X55 in a small techinacl room, in the corner of the house. That reduces the Wifi quality, and instead of old 600mb/s in the living room, I'm getting speeds under 200mb/s, so this is not a good final solution...

I've tried disabling fast roaming and mesh technology, with no help.

 I now tested with Asus ac1750.

Fiber optics modem -> Asus AC1750 (to distribute wired around the house) -> Deco X55

Again same issue. When I connect to the Deco Network I get download 590mb/s upload 0mb/s.

Then running speedtest again, it says no network.

Still Spotify working, browser working. Netflix or any videoplayer not working at all. Instagram working slowly.

So there is some data moving, but working very poorly on the Samsung S24. Every other seems to be working well.

I think this clarifies that using the router before Deco X55 is causing some how the issue, but two routers do the same, so the problem is not with the router it self.

Hopefully you can find a solution, otherwise I need to go with some other brand. 

The mystery thickens...

I went back to the solution that worked, but with slower speeds due to main X55 being in a far away corner.

I connected X55 straight to the Fiber optics modem.

Well surprise surprise, it doesn't work anymore. Acts exactly the same way as with the routers in between.