I don't think many people here are familiar with zmcertmgr or have zimbra installations they can test against. You can search the forums for other threads, and may find an answer there.
There have recently been a few issues with people confused by openssl commands when trying to verify certificates. That is probably what you are experiencing, though it could also be from outdated software on your machine that can not build a proper trust chain.
see Openssl verification fails for Letsencrypt issued certificate