To reproduce:
1. Open attached Unity project "AssetBundles.zip"
2. in the menu bar, click test --> testload
3. Observe "public static load2" function in Assets --> Scripts --> "test" script (starts at line 20)
4. Observe Console

Expected result: All of the children components should be found by their names with LoadAsset(), like they are found with LoadAllAssets()
Actual result: The children are not found (printed out in console as null)

Note: The bug is reproducible with every FBX I tried. I even added a completely unedited blender model "untitled.fbx" and the result was the same. You can check it out by changing line 22 of "test" function from "var fbxBundlePath = "assets/streamingassets/test.fbx.bundle";" to "var fbxBundlePath = "assets/AssetBundles/untitled";" and then clicking test --> testload (see attached gif "untitled.gif")

Note2: This is not a scripting issue, as with another AssetBundle "test2" made completely out of random separate images changing line 22 of "test" function from "var fbxBundlePath = "assets/streamingassets/test.fbx.bundle";" to "var fbxBundlePath = "assets/AssetBundles/test2";" and then clicking test --> testload every object is loaded without any problems (see attached gif "test2.gif")

Reproduced on: 5.6.3p2, 2017.1.1.f1, 2017.2.0b11, 2017.3.0a7