Thanks for playing! Yeah that is a feature; the gate doesn't open until the sheep are all fed and at 100% health. So if they get hurt, they still need to eat to heal their wounds.
I uploaded a new version which would hopefully let players be able to progress through the levels more smoothly. Although, there's still a bug where a sheep can forget to eat and it takes several nudges to get them to find an "available" grass. But nothing core has changed so if you don't want to replay it, that's fine. I appreciate your feedback.