aiProcess_PreTransformVertices causes triangles to \\\"disappear\\\" in Assimp 3.0. Previously worked fine in Assimp 2.0.
Sponza Scene with missing triangles
Are you sure this is related to aiProcess_PreTransformVertices? Does it work without the step? This could be caused by an issue in aiProcess_Triangulate, for which we actually have a related bug report.
It's been a while since I tested it, but I'm pretty sure the flags I used where aiProcessPreset_TargetRealtime_MaxQuality | aiProcess_PreTransformVertices, and it would work without the aiProcess_PreTransformVertices and break with aiProcess_PreTransformVertices. I reverted back to Assimp 2 since that was a deal-breaker for me. Where is the bug report for aiProcess_Triangulate?
Seems to be working on latest version of assimp