smart device connection

[matrex_a1990]

hello all
i have this weird issue still don't know whats the cause for it 

when i try connect smart device like AC, lamp to the WiFi using my phone

some of them connect with wifi but don't work and some of them don't connect at all

i have two router in my house , when i connect them to main router they work fine

but why they don'y work on the second one , this issue happen to me many time and still don't know why

the second router work fine , all phone and laptop work , i try disable wifi security didn't work
i use router static ip , no bridge , my config fine 100% , and the DHCP also fine
try set manual dns my ip router , google router , blank dns 
nothing work

does anyone have idea whats the cause for this !!!

[matrex_a1990]

any reply ?