Are you 100% sure your CA files is in the precise PEM format required by Python for CA certs, as described in https://docs.python.org/3/library/ssl.html#ssl-certificates ?

The most likely cause of your failure and success would be if you were using some other cert format that Windows could load that wasn't PEM.

Also, side-note, you messed up your path when you attempted to anonymize it (you omitted the backslash after C:). Of course, you didn't anonymize it in the error output, so I can tell the original path was not messed up.