When you configure the certificate in the CACERTS instead of upload a p12 in conjur plugin the empty / null value isn't properly managed, in the configure system it seems all the configuration are correct but the pipeline to test secret retrieve in conjure breaks because somehow it seems has the certificate combo-box populated.
As you can see in the image the certificate is none.
Below some instruction on how to configure jenkins
The workaround we found is:
manage jenkins -> configure system -> apply with " - none - " field.
The problem of this workaround is everytime you restart jenkins you need to reapply the configuration all the time.