That's great.
We need modified stages like that.
Reason why objects tend to disappear is, they are made to be disappeared when they got out of your sight.
And the original positions of them were decided by something different factors. (may be bone?)
So if you have moved visible objects only,
when their original points are got out of your sight, they will be disappeared.
There are 2 solutions for that.
1) moving 'the points ' together. I didn't try that.
2) should find an object that never disappears.
One thing I found was sky dome.
if you use your new objects within that kind of object, they will not disappear.
And bad thing about the sky dome was it didn't received body's shadow.
If you can find better object, I hope you can share the information.
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using blender plug-in will change body size of the animation due to the dummy model you were using.
knowing this will help you, I guess.
if you drag your .csv files into Motion CSV Controller, it will tell the center-point coordinate below.
they can be used for handy relocation for another csv files.
or X,Y,Z of the HIP00 in first frame means center point.
Bad thing about my tool is, the object can't be rotated. it can only be moved.
I tried that,.. but it was very challenging mathematically..