I found that the mongodump tool does not like bundled certificates. I was using a .pem file that had the TLS certificate, plus the CA chain bundle of certificates, then the key and got this error. Once I edited the .pem file to only contain the TLS certificate and the key, mongodump worked fine.

The bundle did work with the mongo command though, so I suspect this is an issue only with the mongodump tool. My mongodump tool is version 100.5.2