Why doesn't nmap see all devices?

Question

linux

When you run the script with the code nmap -sP 192.168.0.*as root, there are about 30 hosts. When running the script with Asterisk around 20... what could be the reason? Maybe nmap doesn't have time to finish searching? Maybe because the users are different?
I wanted to get a list of PCs on the network.
upd: 2017.07.05 11:06
As it turned out, nmap under the asterisk user behaves differently than from under root.
Probably not enough rights to work with the network or something ...

Answer 1

Not all hosts can respond to a ping

nmap -sn 192.168.0.0/24