ᐅ New Cheminee Frei Oeko Plus 75 x 57 F+ is producing smoke

Instead of the 30-year-old open fireplace, we had a new Cheminée Frei Oeko plus 75 x 57 F+L installed. When operating with the door open, an unpleasant smoke smell soon spreads, which after no more than half an hour requires closing the door and intensive ventilation. The fireplace installer says we just have to live with it and use it with the door closed, or have a new chimney cap installed to improve draft. Some additional information:

• The old fireplace had very good draft and never caused smoke odors
• The draft in the new system is also very good
• The manufacturer explicitly allows operation with the door open in the user manual and even sells accessories for grilling...
• An external air supply is installed
• Smoke emission is constant and independent of weather conditions

The smoke appears clearly ONLY when the door is open and ONLY from the gap between the door and the outer wall of the insert. It seems that inside the firebox, “swirling” currents develop that cause the smoke to move along the inside of the open glass door, then creep along the door, descend on the outside, and enter the living space. We therefore fear that the proposed draft improvement is not the cause of the smoke leakage.

Does anyone have any advice? Is this not a design flaw of the insert? Do we really have to live with it?

Thank you very much for your help.