Sorry for the delay, Eric Tamez, I'm told Support has a call scheduled with you today (Thursday, May 19th). If you get a resolution, I hope you can come back and let us all know what it was.
Your community manager
In my case the issue is related to expired authentication in the browser.
A different way to reproduce it, is to use the Page Viewer Web Part with the New Form link of the form's list. The result (when the authentication expires) will be white content in modern browsers and for IE it will be "Content cannot be displayed on a frame". That's because the form is trying to send the user to the authentication page and since the Web Parts are using an iframe, the display of the login page is blocked due cross domain restriction.
1.- Force the page to request the user to login.
2.- Close/open the browser or open a new session.
@Tomasz Poszytek, It has been a while since I looked into this. As I recall correctly, the problem was fixed after a new update of Nintex Forms for Office 365 was launched. After that, I was able to add the List Form Web Part without any problems.
Unfortunately I am not the right person in this case. The right address to report such behavior and to look for assistance is firstname.lastname@example.org<mailto:email@example.com>. This possibly can be somehow debugged by the dev team of Nintex.
On the other hand, have you tried to use other we browser? Or/ and to clean up cache, cookies and temporary files?
tel: +48 603 993 372
www/ blog: https://poszytek.eu
I added the sites below to the browsers trusted sites and my issues with Nintex form and workflow got resolved... to me the first 4 should be enough but I added all of them!!!