In 4.9 and 4.11, animations import correctly.
In 4.10, both my shoulder joints import with a value of 0 on one of the rotate channels. As far as I can tell the shoulder joints are the only joints affected.
From left to right: The animation in Maya before export (correct), the animation in UE4 after import (incorrect), the animation exported back out of UE4 (showing the mysterious 0 angle) (incorrect), and the exported .fbx imported back into Maya before going into UE4 (correct).
This means that the issue happens on import into UE4, and shouldn’t have anything to do with the .fbx exporter settings.
I’m using .fbx 2014, all joints are keyed every frame at 30 fps, there are no constraints, and I’ve used every combination of export and import options in UE4 with the exact same results. I’m not using the UE4 animation and rigging toolset, the rig is completely custom. No special attributes are exported or imported, just the pure bones and their rotates. The issue exists in 4.10.2 and 4.10.4, but not in 4.9.2 or 4.11.0 Preview 7. I get no error messages on importing the bind pose or the animation.