The library ODDT, which includes PLEC, throws an error when reading a PDB file that contains HIE residues. ODDT can use both openbabel and RDKit, but the error only occurs when ODDT is using RDKit.
The error actually is introduced by ODDT, where a function of RDKit is redefined in order to "fix" double bonds in special residues such as HIE.
I have included a notebook and a PDB file where I show how to reproduce the error.
Bonus: it turns out that openbabel is much faster than RDKit in reading from PDB file.
ODDT_HIE_bug.zip