Sorry I don’t understand what you are doing here exactly. Do you create a credential via python-gvm and are using it as a credential for authenticated scans and this leads to the posted error? You have listed an error log from the scanner which isn’t related to python-gvm. python-gvm talks to openvasmd/gvmd. See
So maybe you have discovered an issue in a nasl script or openvassd directly. But most likely it is not related to python-gvm.