Why do my wireless 4K boxes have weaker signal than my other streaming devices

I have Xfinity X1 with 1 wired 4K box and 2 wireless 4K boxes. I also have 3 apple TV boxes throughout the house. Both wireless boxes are within 15-30 feet of the wireless gateway and while other devices register strong signals the wireless boxes cannot seem to get full strength and show 1-2 bars on the signal indicator.

When wireless boxes are in use one of them sometimes freezes even when the apple TV sitting right next to it is running strong with a strong signal strength. Is there something that is causing a lower signal strength/speed to get to the wi-fi boxes vs. the other devices? One of my apple TVs sits on the opposite side of the house as the wireless gateway and still never drops signal vs. the 4k wireless boxes which drop frequently and require restart.