We're using a custom AssetPostprocessor to automate setting up ModelImporter.extraExposedTransformPaths. The way we do this is by iterating over ModelImporter.transformPaths, checking for names and then assigning the resulting list to ModelImporter.extraExposedTransformPaths. This worked flawlessly until Unity 2018.2.20f1. Now, after upgrading to Unity 2018.3.3, transformPaths always returns an empty list and our asset post processor breaks. The transforms are shown correctly in the inspector UI, with fancy checkbox-tree. I've tried several things to fix / work around this issue: Moved the code from OnPreprocessModel() to OnPostprocessModel(), set dragonImporter.optimizeGameObjects to false ... but so far, no matter what I do, transformPaths always is an empty list. Any ideas what is the issue with this, and how I can solve it?