Three.js calling clipAction.play() makes animated objects vanish - three.js

Question

In Three.js, Calling action.play() makes objects just vanish, without any error or warning on the console.
I use THREE.ObjectLoader to load a JSON file created in blender. The srt (position/scale/quaternion) animation is in the generated file. As are the morphtargets. To optimise filesize I animated the srt as a series of null objects. The morphtargets tracks are in the main object, which I clone 5 times to build the characters (balloons to be exact).
I previously did extensive testing to introduce shape/morph animation. After being succesfull I finalised all the animations. Only to be trumped by the disappearing models. The srt (position/scale/quaternion) animation was working fine before. But after refactoring the code, to be less spagettied, upon calling action.play(). The objects just vanish, exactly then. Echoeing the mixers and the array containing the clips, everything looks correct (ie I see the tracks, the names are right etc). Also examining the newly generated JSON, it seems the same and correct (also I have not changed the SRT animations, only introduced shapeanimation)
So I am lost, and think this looks more and more like a bug. From previous experience I do know it works (or has worked).
I created a jsfiddle: https://jsfiddle.net/oompol/3ya6sqed/
[edit] I turned on the action.play and call the function from the link in the div [/edit] please note I commented out calling action.play(). So you see the load and init work. See the function listed below
function playScene(scene) {
for (parentName in srtMixers) {
var clpName = "balloon1_fly";
var clp = THREE.AnimationClip.findByName(animLib, clpName);
var action = srtMixers[parentName].clipAction(clp);
action.clampWhenFinished = true;
console.log("playScene:", clpName, clp, parentName, srtMixers);
//this is when the problem happens
action.play();
}
}
This is the JSON I am loading:
https://rawgit.com/bakajin/2e3d2f6a722103ed4aefd76f6250ec08/raw/28cad35c20060d478499c0cd40a2753611993720/oomp-scene_balloons-oomp-6.9.4.json

Answer 1

Ok,
there was something very wrong with the scaling indeed.
The io_three JSON exporter for Blender (r87 dev) writes incorrect matrix transformation data in the geometry object (really tiny scaling values). The animation track with the scaling keys were correctly written as 1,1,1. So all the objects just scaled out of view immediately.
Hard to see because the geometry has no separate scaling value but a matrix. Seems to happen when you set "Scene" to true on export.
Worked around the problem by entering the scaling value in the keyframe tracks. But this will only work if you have no scaling animation (so the keys are all one).
Meanwhile I have extensively edited the JSON by hand. Because this is not the only incorrect data. The formatting of the animation object is also wrong. The durations for the morphTargetInfluence Keys is also incorrect. The formatting of these keys is also not always correct.
Hope this helps some other ppl