There’s nothing wrong with your IFC or Speckle Objects. Simply, there are a few property types that IFC & Speckle supports, that Blender doesn’t support attaching as custom properties.
Those properties are visible here, and accessible via python scripting.
It looks like blender only supports the following types: int, float, string, int, float
With my fix, any property with unsupported types will now simply be ignored, instead of it causing the whole object to fail to be converted. 
e.g. I see some polar coordinates (int) fail to attach.
If you really need those properties, you can always inject a python receive script to re-attach those properties see Get window dimensions in Blender - #5 by gokermu
But most users just care about getting their geometry into Blender, the properties are a 
on top.
This would be a fix just to the Blender connector