Hey Tim,
Thanks for the advice ! It worked as soon as I unticked “render in main pass” on the first copy but the reflections vanished with building the scene… I tried and tried and it did not stand the lighting build. I updated the reflection captures in the meantime with no success.
This gave me an idea though, I checked back the “render in main pass” box and unchecked “cast volumetric translucent shadow” instead on the first instance and it worked as intended. However, the two objects were adding opacity to each other so I had to tune down transluency and put some more white color on my glass material to obtain something believable.
To sum it up, I now have two sames meshes on the same spot, original one showing reflections (Volumetric Translucent shadow off) and the other acting as a shadow caster. Here is what I came up with :
As you can see, the result is close to yours, but some of the triangulated geometry is now visible on the far left of the pot. I know for a fact that glass is the nightmare of all 3D artists, but a few improvements in this area would be a major step in Archviz on Unreal Engine.
This problem is resolved for me, unless you may have some more tricks to share 
Thanks again for your help.