PABretherton
I've analyzed your JSON.
The problem is related to the Base/Neck
transform constraint that is enabled when Strap_01A
, Strap_01B
, or Strap_01C
are enabled.
The Head
bone is a child of the Neck
bone, which is a child of Body_T1
. Also note that Body_T2
is a child of Body_T1
.
The Base/Neck
transform constraint connects the source bone Body_T2
to the target bone Neck
.
This means that when this transform constraint is enabled, the Base/Neck
follows the transform of Body_T2
, since in the JSON you sent us, all transform mixes are 100%.
The 2_Idle2
animation animates the scale of Body_T2
, and consequently the scale of Neck
and Head
is changed too.
I bet that in the 4.3 editor you didn't connect the scale of the source to the scale of the target, but the JSON export from the 4.3 editor into a 4.2 JSON creates the transform constraint enabling all connections.
You can fix the issue by setting the mix of the scale X and Y to 0 in the 4.2 editor, then exporting the JSON again.