sim unlock window not appearing.

Hey,

I work in a repair shop and we repair ipads for a company, Recently 5 ipads came back to me with all the same issue.

The issue is really strange, some popup windows never appear which makes

it that i cant unlock simcards with a code. When i put my simcard in it (i removed the code) it works without any issue. I tryed to reset the ipad on i tunes after this it still didnt work. Even in the activation menu it still did not ask for the sim to unlock and i had to proceed with my own sim. Also called with a motherboard specialist and he didnt even hear about this issue. Any one of you guys knows what this could be?