Guest network reduces WiFi range!

[Minglarn]

I've been looking for a "repeater" for a while now as my WiFi dont reach out to my parking lot witch is about 20m away from my RT-N66U (behind a couple of walls). Since the first day I installed my router I've enabled the guest network so my friends could access my fibre.

However, today I disabled the guest network by accident and left it off for a hour or so and noticed that I have full reception on my parking lot, confused and happy I sat down and checked all my setting and realized that disabling my guest network has gained A LOT in range for my WiFi, as soon I enable it I loose connection on my parking lot.

Why?

Edit:
Firmware:374.42 (Merlin build), 1 SSID on 2.4gHz and 1 SSID on 5gHz.

 

[KGB7]

A while back, another user had better WiFi speed on guest network. Don't recall why, so you'll have to search for the thread.

Try another firmware.

 

[Minglarn]

Ok, I'll try to install .44 and check if I notice any difference.