Without a URL we couldn't possibly troubleshoot this for you.
The cookie value you've shown is designed for the marketo.com domain. That cookie would not be generated on an external website.
Try having a hidden email field on the 2nd form so the two leads get merged by email address. There are many ways you can achieve the end result. 2 simple ones below:
1. In the first form, using marketo forms onsuccess method, manually overwrite the followup page url while appending an url parameter with the value of the email field, have the hidden email field in the second form read from the url parameter
2. In the first form, using marketo forms onsubmit method, save the value of the email field to a cookie, have the hidden email field in the second form read from the cookie
You still haven't provided enough background.
You aren't running Munchkin at all on these pages and you haven't explained why. (In fact, there are no cookies set, so you can't use the automatic persistent session association that comes with Marketo forms.)