I had a very similar problem (with bionic). I was able to upgrade to FreeIPA 4.3.1 by installing version 3.36.1 of the package libnss3, from the cosmic repositories. There is a bug in the version 3.35 distributed with bionic (see https://bugzilla.redhat.com/show_bug.cgi?id=1568271) which prevents upgrades (and not only... installing a replica IPA server was also failing for me).
I had a very similar problem (with bionic). I was able to upgrade to FreeIPA 4.3.1 by installing version 3.36.1 of the package libnss3, from the cosmic repositories. There is a bug in the version 3.35 distributed with bionic (see https:/ /bugzilla. redhat. com/show_ bug.cgi? id=1568271) which prevents upgrades (and not only... installing a replica IPA server was also failing for me).