Some tablets respond to pings, others don't

There are dozens of tablets on my table that are all connected to the same 5GHz Wi-Fi network. All IP addresses were given by DHCP in subnet

.168.34.0/24

. I want to find the ip addresses of all of them so that I connect to them and use

wirelessly. After unlocking all devices and making sure they had enough battery, I tried

nmap -sn 192.168.34.1-254

. While it found a majority of the tablets, some were missing. Then I tried a broadcast ping with

192.168.34.255 -b

but got zero responses. However I can manually pick up a tablet, go to its settings find its ip and ping it manually and they always respond. For instance

.168.34.123

was not found by

but

192.168.34.123

always works. Why do some tablets not respond to nmap pings but do respond to manual pings? How can I ensure that all tablets are reachable by

? Are there other commands or tools that are more suitable for the job?