The likely cause of the issue of weak Wi-Fi coverage in the office is that the AP is using a directional antenna.
A directional antenna is an antenna that radiates or receives radio waves more strongly in one or more directions, creating a focused beam of signal. A directional antenna can provide better coverage and performance for a specific area, but it can also create dead zones or weak spots for other areas. The other options are incorrect because they eitherdo not affect the Wi-Fi coverage or do not match the scenario.
References:
https://www.arubanetworks.com/techdocs/ArubaOS_86_Web_Help/Content/arubaos-solutions/wlan-rf/rf-fundam