this is a clean zabbix install using only default hosts.
there are a few problems with "hosts info" screen element :

1. selecting "- all groups -" shows as a title for the hosts info : 'Hosts info for node "()"'

2. hosts info for all groups shows
"12 Available 0 Not available 252 Unknown"

reports -> Status of ZABBIX shows :
Number of hosts (monitored/not monitored/templates/deleted) 22(1/0/21/0)

3. selecting group "linux servers" (where there is a single member, the monitored zabbix server) shows :
Hosts info for group "() Linux servers"
0 Available 0 Not available 0 Unknown

note the parenthesis and 0 hosts shown.