We allow formed patties to rest and chill for at least 30 minutes in refrigerator after forming.
They will stay together better on the grill. Just plain, freshly ground meat here, no other ingredients.

Restaurant trick is to press a thumb in center of patty to form a concave depression (both sides).
When cooking, it will plump up, and flatten out.
Otherwise, will have a convex shape after cooking and not sit well on bun.