I solved the problem of the mysterious graphic effect.
On the advice of angrypig I reviewed all rotation commands of the script of my model "normalizing" the axis of rotation to the values of "zero" and "one", and everything started to work perfectly.
Put simply, for the interest of someone reading this post, things work this way:
The command geom :: rotate_joint_orig you write:
..... geom.rotate_joint_orig (bone_id, valrot, {x: a, y: b, z: c});
bone_id is the object to rotate
valrot is the angle of rotation in radians
a, b and c are the values of the rotation axes x, y and z
Before they could give no unit values to the variables a, b and c and it could lead, in a single command line, a differential rotation on three axes,
now (since version 5819) a, b and c can only be "0", "1" (and maybe "-1").
For example:
Before: geom.rotate_joint_orig (bone_id, 1, {x: 1.75, y: coeff * 15-dist, z: c});
Now: geom.rotate_joint_orig (bone_id, 1.75, {x: 1, y: 0, z: 0});
geom.rotate_joint (bone_id, coeff * 15-dist, {x: 0, y 1, z: 0});
geom.rotate_joint (bone_id, c, {x: 0, y: 0, z: 1});
I hope to have understood the directive angrypig (ask confirmation or correction)
However this all works well.