Google adsense not showing ads consecutively

i have integrated google adsense for my client's website, ads are showing in some devices, but in some devices it showing always, particularly ads are not showing always in my client's devices,

is that any mistake i did on my google adsense account to resolve this issue, or it is the nature of google adsense?

but client's want to get ads for all devices and every time it need to show on his website,

i have tried with lots of blogs about this, everything is failed, and i'm finally here, hopefully i get a valuable knowledge here,

this is my first question on stackoverflow, if i made any mistake on it, please don't mind it, i'll correct on my future questions.

Thanks in advance.