Timestamps broken on interest list

Title: Our site has a very simple sign-up form to collect emails for people interested in our product launch. They visit the site, put in their email address. We have a google (spread) sheet that's connected to it. The way it was working recently was that a user would put in their email address and it would populate on our sheet along with a time stamp. That's not working anymore. The email address still populates but the timestamps don't anymore.  

thank you! trying these different tips seemed to have done it!