I used to have same SSID for both my 2.4 and 5 Ghz network and let the device choose accordingly which one to connect to.

I noticed then that the 5Ghz network didn't have any hosts connected lately, initially I thought it was just coincidence but then after a few days I decided to give different SSIDs to the networks and seen that the 5Ghz one didn't show up.

I've already tried to unplug the router for a few minutes and factory reset but none of these things worked.

Any suggestions?

Edited:

I've noticed that moving the 5gz antenna, the network goes back and forth. Can it be hardware related?

It's not hardware related because I had it replaced and although 5ghz is on none of my devices detects it.

Solved, it turned out that an object I had near the router was somehow blocking the 5ghz network.