The update comment blames glycol contamination...
From Youtube:
Stephan Segraves
259 subscribersThis United 777 was set to leave Chicago O'Hare for Honolulu when it hit a small snag.... Being too heavy for the tug. And then being too heavy for the second tug. If you want to see how this ends:
https://youtu.be/QqqAZKCStF8
[UPDATE] Apparently a lot of this has to do with glycol being on the ground and not with the weight of the plane. It still strikes me as odd that the ground crew tried to use a second tug to push the plane back.