Getting the same issue with my sites. I presume it is something the systems admin needs to look at. hoping to get some info to him on a fix. I had one successful install, then the others failed.
Ok I resolve it to upgrade letsencrypt-cpanel.x86_64 to the Latest version 0.6.5.
You can upgrade via this command
yum clean all && yum -y install letsencrypt-cpanel
or if it does not work, download the rpm and upgrade it manually
Guys and gals, if you are having difficulty, please contact us at https://letsencrypt-for-cpanel.com/contact , this community is not a support channel for the plugin. Thanks.