Hi All, below is my osticket installation info

I have quite a long form users need to fill out on my osticket portal page. Sometimes, my user work half of the form and leave it for a while. When they return, they finish fill in the form and then click submit, some of the details are disappear and this error prompt (although they have finished fill all the details)

Need your advice why it happen this way? and is there a way to increase the timeout time on the user portal?