@RafaelA ,
I apologize for the late response and I am glad that you found the culprit.
It seems that this issue comes about not because of code in the Load HB Objects component but rather code in the Dump HB Objects. Specifically, there is a check to see if the boundary condition is of a certain type in this component, which is written in a way that only supports the 4 current Honeybee Boundary conditions. This does unfortunately mean that, if you have a already have a custom-bc model written to .hb format with the Dump Honeybee component, there is no easy way to get it back (the only way that I can think of is if you try to edit the .hb file in a text editor and try to replace parts that reference boundary conditions but this is pretty difficult given that it is a compressed format).
The good news is that it is very easy to make a Dump Honeybee Objects component that supports the writing of these custom boundary conditions into the .hb file. In fact, all that we need to do is edit that one check and it can be done in a way that does not interfere with the current functionality so I just push this change to gihtub:
You can see a working example with your special ground boundary condition here:
custom_boundary_conditions.gh (476.9 KB)