I've put together a new form and a people picker control will not work unless the person opening the form has default SP level - contribute access to the list. (Historically I've created a permission level contribute, no delete).
Likewise on the same form, I have a list lookup control which will not resolve the list unless the same person has contribute to the list being looked up. Surely read should be enough?
I also added a calculated value on the form to check which user the form thought was opening the form.
I replaced the controls, in case something funny was going on with the controls.
Nintex Forms 2013 ( 18.104.22.168 )