Employee vs. Employer Contributions
A common pitfall in dividing a 401(k) is misunderstanding the difference between contributions made by the employee and those contributed by the employer. A good QDRO makes clear whether both types are being divided proportionally.
In many plans, employer contributions are subject to a vesting schedule. If the participant spouse has not met the service requirements, some employer contributions may be forfeited. These cannot be divided with the alternate payee. Your QDRO must account for forfeited or unvested funds.

