Employee and Employer Contributions
Most 401(k) plans include both employee contributions and employer matching or profit-sharing amounts. A QDRO must be very clear about whether both types of contributions are included in the award to an alternate payee (usually the ex-spouse).
Employer contributions can have vesting schedules that delay ownership. If the participant spouse isn’t fully vested at the time of divorce, the non-participant spouse may lose out unless that’s addressed in the QDRO terms.

