If the mix is set to 0 in the setup pose, the physics constraints will not be applied correctly to the exported animation.

[misaki-eymard]

Description:
If the mix of the physics constraints is set to 0 in the setup pose, even if you change the mix value in the animation, the physics will not be applied correctly in the exported animation. The value 0 is important, and if the mix is a value like 0.001, for example, the physics will be applied correctly during the animation. This problem occurs when exporting animations in formats such as animated GIF, AVI, or MOV. This problem cannot be solved even if you apply Warm up.

Expected behavior:
Even if the mix of the physics constraints is 0 in the setup pose, if the mix value is changed during the animation, the physics will be performed according to that value.

Steps to reproduce:

1. Open the celestial-circus-pro.spine with Spine 4.2.
2. Select physics constraints swing-top, swing-bottom, and bench-front under the Constraints node, and set the mix to 0 in the setup mode:
   
3. Switch to the animate mode and add keys with mix:100 for the three bones at frame 0 in the swing animation. The result of playing the swing animation in the editor should be like this:
   
4. Export the swing animation to an animated image or video format such as GIF, AVI, or MOV. You should get the following result:
   

The version of Spine in which this issue was found:
4.2.00, 4.2.36

This issue was reported in the following thread on the forum:
https://esotericsoftware.com/forum/d/26897-exporting-animation-with-physics-constraints-keyframes-breaks-the-contraint