TP-Link Archer D20 (Guest mode problem)

I bought Archer D20 from amazon a week ago. Everything works fine except guest mode on 2.4 GHz band. Whenever there is a power cut or router reboot, guest mode SSID disappears. Strange thing is this doesn't happen on 5 GHz frequency. Also when I make the guest 2.4 GHz SSID open with no password it shows upon reboot. Any solution to this strange behavior? Another thing I noticed is that when I turn off the bandwidth control for guest mode and encrypt the 2.4 GHz guest network, it works as expected.