Let's try to check first what causing those hosts to show 0% connectivity by checking the processes connectivity.
Can you please show the connectivity of the processes of one of the hosts with 0% connectivity, sort the processes by the connectivity to see which of the processes are refusing connection ...
And also take a look a this thread which explain what is the meaning of Host connectivity metric.
Hello @Yos N.
Than you for sharing the thread.
The below host showing 0% connectivity while you can see that maximum retransmission is 0.85% for one of the following processes, but the connectivity is 100%.
The host which is showing 100% connectivity has a maximum retransmission of 0.93% for one of the processes.
Ammm its look like the blame here is on Host connections good question for dynatrace one I think