Double click the yellow triangle and see what it says - may or may not be useful.
I had this error with a file and it came down to a corrupt 3D element.
Do you get any error messages when viewed in 3D in Archicad?
The problem I had was a painting object on a wall that could not find the associated JPG image for the painting.
I deleted that and all was fine with the BIMx model.
I isolated the problem by turning half the layers off and generating the 3D model.
No problems then turn half of the remaining layers on and generate BIMx again.
Keep doing this until you can find the layer causing the problem, then you might be able to see the problem in Archicad.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11