This page explains symptoms experienced with Host monitoring
If the host is active check that the interface selected for Highlight exists and is correct for the host in question.
If the parent bearer watch is green in Highlight but the Host watch is showing red timeout issues, this is likely to be the host device not responding efficiently to SNMP GETBULK requests
Check if there is a more recent version for the SNMP application running on the host and update if available.
Unlike other autodiscovered elements, host disk information is only collected every two hours so there is likely to be an initial period when CPU/memory detail is displayed but there is no disk information.
There is no action required