To reproduce:
1) Download attached project
2) Before opening it, shorten the path a bit or otherwise build process will fail as it won't be able to locate files too deep in hierarchy
3) Open the project and Assets/MainScene
4) In top bar menu, select "Portfolio -> Assets Bundles -> Force...." and "Portfolio -> Build Viewer (Release)"
5) Open IIS
6) Make two sites:
a) Asset Bundles Server - Path: <project_path>/Servers/AssetBundles - IP: All Unassigned (so localhost) - Port: 82 (Editor testing is set up for localhost:82)
b) Viewer Server - Path: <project_path>/Servers/Viewer - others however you wish
7) Play the scene in Editor, click "U" when loaded and prompted, select either Redpaint or Aluminum (what I tested with)
8) Open Viewer Server in browser, and do the same as step 7 there
9) Compare results

Expected: Both views look the same
Actual: In editor, there is no metalness to material

Reproduced in 5.5.0p1, 5.5.3f1