UTM Values Not Capturing Consistently

I am capturing UTM parameters in hidden fields on Marketo forms via cookie.  Recently we noticed that known users UTM values are not being captured in the hidden fields even though the UTM parameters are in the URL.  We reviewed the java script for the cookie code and its storing the values.

After 3 form submit attempts, none of which captured the UTM values, I used Chrome Incognito with the same URL/UTM parameters and this time it captured the UTM values in the hidden fields.

Anyone run into this issue?   I spoke to Marketo support and we changed the Pre-fill for the hidden fields from enable to disabled, I thought that would fix the issue, however after testing still running into the same issue.

#tracking utms