How many triangles are supported by UE4?

hi everybody, i wonder how many triangles are supported in UE4?
i have developed a plugin to import CAD model into UE4–similiar to Datasimth in functionaity. Everything goes well when importing and rendering simple CAD modle, but one of my CAD model is very complex which has more than 4,000,000 facets, more than 3000 actors are created in UE4 level( some of these actor are empty and has no mesh), it can be imported into ue4 and displayed in the Viewport, i can translate and scale the model in viewport like other normal actors, but the engine crashed when “Play” button is clicked (switch to Paly In Eidtor mode) and i got the error message like:

LogWindows:Error: Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\Build\++UE4+Release-4.13+Compile\Sync\Engine\Source\Runtime\Core\Public\Containers\Array.h]LogWindows:Error: Array index out of bounds: 2147483645 from an array of size -2147483648 (2^31, and the type of ArrayNum is signed int32, its overflow to negetive)

Then I deleted about 500 of 3000 actors from the level, it works very well and engine does not crash. Afterward, I imported a other less complex CAD model and it also works well.
So i am sure the reason why this crash occurr is there are too many actors or triangles in level.
But i am confused which array has a length more than 2^31 while my triangles and vertex is just about several millions and how many triangles are supported by UE4?

You need to use a low poly model and use a Normal map from the high poly model to make your game run faster