Troublesome token content was one of two prerequisites for string invalidity. Each invalid SELFIES contained at least one troublesome token whose bond count exceeded valid valence in the converted SMILES. Hence, troublesome tokens alone were insufficient; their atomic neighborhood also contributed. Indeed, 13.1% of the VAE's valid SELFIES contained at least one troublesome token. By tracing conversion logic, we observed that the SELFIES module successfully discarded troublesome tokens or their neighboring tokens to introduce a disconnection point in the valid SMILES. However, the conversion module could not universally correct valences/charges associated with the two troublesome atom tokens. By contrast, SELFIES demonstrated 100% robustness for generated strings without troublesome tokens.