Make sure hostname is good:
/usr/local/cpanel/scripts/check_valid_server_hostname
Did you run /scripts/upcp –force? If not do it.
/scripts/upcp --force
If you run it already, run it again as I got this fixed after the second run.
If still not working:
cd /var/cpanel/.application-locks
rm -fv UpdateHostname\:USERNAME
/usr/local/cpanel/bin/update_horde_config --user=USERNAME
where USERNAME is cPanel username.
Source:
https://forums.cpanel.net/threads/horde-wont-load-after-update-to-11-52.503071/