... we found that the six library does a check when reading a CPHD file to ensure that the Release Info field not only exists, but that it is not an empty string. The CPHD spec does require that the field exists, but does not seem to prohibit it from being an empty string.

We have gotten some vendor CPHDs with an empty field here and have failed reading the file due to this. I checked and SARPY is able to read (it must not implement the same check). ...