Uploading an FBX with time range starting at a negative frame causes the SyncSketch timeline to be offset, causing some very odd behaviour.
(i.e. FBX with data frames -50:50, will have the anim in SyncSketch at 1:100, but the anim will have some odd behaviour)
Ideally the SyncSketch timeline it would match exactly what is in the FBX, so when doing review/feedback we can call out what precise frames need attention.
Luke M