This bug has been documented in the forum already:
Problem:
In Pro, the form in the classic gravity forms module/element has been unset when updating from Pro 5 to Pro 6. It appears to be only happening on the first form listed on the Gravity Forms Classic dropdown. The contact form must be reselected within the Pro dashboard for the form to display properly.
With the update, we have a multitude of sites needing to have this form reselected, so much so that reselecting the form in the Pro dashboard in all of the sites is not feasible.
What is a possible solution for multiple sites needing this fix?
Thank you.