This issue seems to be depending on the network / DNS config in which the icinga2 machine is currently running.
All other views / menus in icingaweb respond quite fast, no matter in what network the icinga2 test machine (ubuntu 18.04 VM) is currently used.
There is no load peak during loading the host view.
I noticed, the the hosts view can take up to 2 minutes to load, but other menus load instantly.
Including the service overview for one host
Then again, the detailed service view is as slow as the host view.
Same for custom defined service checks
or service checks that are included in icinga2
Since the DB calls run on the same machine, addressed to localhost, which parameters in the network configuration could affect the internal queries from the icingaweb UI to the stored data ?