If the bolt attaching the seat tightens too easily, it is not in the hole and rests above or below the wood of the seat. This is what causes the tipping or dipping of the seat.

When attaching the bolt for the back of the chair, insert a plastic washer between the wood of the chair leg and the wood of the chair back. Without this washer, the two pieces will not sit flush. This allows the chair to shift and may cause the chair to become unstable.