This may happen due to signal loss because of obstacles and or/distance.

The maximum reported signal transmission distance assumes the absence of any interferences, as it is measured in laboratory environments.

Thick walls, the type of wall, radio frequencies, Wi-Fi devices, etc, can cause disturbances that affect the quality and range of your signal.

Here are a few examples of signal loss according to types of walls:

a) with a concrete wall, the signal loses between 50 & 80% of its intensity;
b) with a brick wall, the signal loses between 30 & 50% of its intensity;

c) with a plasterboard wall, the signal loses between 30 & 40% of its intensity.

You can always, however, purchase a signal repeater/amplifier to tackle these issues.