I created the simplest possible avatar, by adding an Avatar Descriptor and an Animator to a cube. I then added a custom FX layer, an Expression Menu and an Expression Parameters object.

The resulting avatar can be tested and uploaded, and the custom parameters show up in the debug menu, but the expression menu is completely empty and the animations from the FX layer are not visible in the debug menu. Strangely enough, the logs contain a line about an SDK2 avatar descriptor? This avatar was built with the latest SDK 3.4.0-beta2 from the VCC, so this might be related to the problem.