Enrique Pérez Arnaud has asked me to draw attention to notes he added to a pyFF gihub issue, regarding duplicate entity ids in pyFF in different federations. The notes can be found here: https://github.com/IdentityPython/pyFF/issues/289#
I will also add this link to the discussion of this issue in the IdPy developers meeting yesterday. The notes from that meeting will be out later today.