Employer Contributions and Vesting Rules
401(k) plans frequently include employer contributions, often matched or discretionary. BUT — not all of these contributions are fully “vested” when you divorce. Any portion of an employer’s contribution that’s unvested at the date used for the division (usually the date of separation or divorce decree) is not marital property and may be forfeited.
Make sure your QDRO clearly distinguishes between vested and unvested employer contributions. If not, this could cause the plan administrator to reject the QDRO or delay processing significantly.

