investigate on load_frm_dict

est/core/types/spectrum.py

@@ -345,7 +345,10 @@ class Spectrum(_Spectrum_Base):
                     value = ddict[key]
                     del ddict[key]
                 else:
-                    value = ddict["_larch_grp_members"][key]
+                    try:
+                        value = ddict["_larch_grp_members"][key]
+                    except Exception as e:
+                        raise RuntimeError("Fails with key", key, "type", type(key))
 
                 larch_ddict[key] = None if value_is_none(value) else value