I answer my own question, it could be useful to a future user :
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First, I tried to reproduce a basic snow emitter (found in this tutorial : PTV Unreal Engine 4 Particle Systems Tutorial 1 (Let It Snow!) - YouTube). The original emitter works with Global Vector field, but not my copy. Finally, it was besauce I didn’t enabled “set fixed bounds” in the top menu (even if I checked “Use Fixed Relative Bounding Box” in Particle system details). After fixed bounds enabled, GBF was recognized.
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Then, when I tried to apply this discovery to my working emitter, I got stuck again. The particles didn’t reacted to GBF even with bound fixed. It was besause I had “Use Local Space” checked in Required module details of the particle.
Finally, it works like a charm !