I’ve reviewed the configuration and seem to have gotten SSL working by removing the <IfModule mod_ssl.c> and </IfModule> lines in /etc/httpd/conf.d/domain1-le-ssl.conf.
I’m not 100% certain, but I think this might be due to the fact that mod_ssl is enabled through /etc/httpd/conf.d/ssl.conf, which might not included before /etc/httpd/conf.d/domain1-le-ssl.conf, so when apache evaluates that file, mod_ssl might not be loaded yet. Either way, this seems to make it work.