it would be helpful if you could add some information about your scenario. What Version of Nintex do you use? 2013? 2016? Office 365?
If on prem, did you update your Nintex installation to the latest version available?
Also, do all Nintex forms don't show after task completion or is it one specific form?
The version is Nintex 2013 on premise. We have not done any update as it will need some more approval on server side.
And yes, none of the forms are opening in IE.
Do other browsers render the form correclty?
Also which version number of Forms are you using right now? Did you check if following patches might adress the issue?