Metals can reflect, shield and absorb 2.4 GHz wireless signals; it is therefore recommended that there are no metal enclosures or walls obstructing the path between the device and the gateway.
Notes
4G has a longer wavelength and slightly better diffraction properties, so a small amount of signal can pass through gaps in metal;
5G has a higher frequency and shorter wavelength, so even a slight obstruction from metal will result in a loss of signal.