@Sinion 

Can you install a software on one of your client devices that allows to scan for and display information about nearby Wi-Fi networks? This should tell you if your AX50 is transmitting on 2.4 GHz at all. Provided you are close to your AX50, the Wi-Fi network(s) with the highest signal strength should belong to the AX50 (also verify the vendor is shown as TP-LINK).

On a Windows computer you could do this with a free software called "Acrylic Wi-Fi Home" or on an Android smartphone try the free App "WiFiAnalyzer", for example.

@woozle I did as you said and I installed the wifi analyzer on my android phone and the funny thing is even though I'm right next to the router, the app shows that I'm 40 meters away (2.4 ghz). Whereas the 5 ghz shows I'm 0 meters away (as it should be)

Any advice?

@Sinion 

I don't know what would cause the distance value to be incorrect by such a big amount.

Are you aware of any other devices nearby that might be causing strong interference on the 2.4 GHz frequency range?

Anyway, the ultimate test for your situation would be to reset the AX50 to Factory Defaults, carry it to a place in your home that is farthest away from the current location, power it up with only the power supply connected and then try to connect to the default SSID (TP-Link_...) using the password printed on the underside of the router.

If your devices still can't connect, then your AX50 is probably faulty.

By the way, having an USB 3.x device connected to the AX50's USB 3.0 port can also make the 2.4 GHz Wi-Fi go bad.
If such was the case, the full configuration GUI (has to be opened via Browser) has an option called "USB 3.0 Interference Reduction" that, if enabled, would switch the USB port to USB 2.0 mode instead.