Thank you for filing this report. I need more information before we can investigate.
Could you share a project file with me that demonstrates the problem? You can send it to me via a DM on this forum if you do not want to post publicly.
A few things need clarifying:
Which composition 3D renderer are you using? If you are using Mercury 3D, please be aware that depth of field has not yet been implemented.
How are you generating depth of field? Via a 3D camera or an effect?