Your network is probably configured with inconsistent subnets / netmasks. iOS / Android are on WiFi and getting a different subnet/netmask than your severs.
Edit: What does pinging the server with nmap mean? Are you checking open ports or pinging the server? That doesn’t make sense or at least leaves us with more questions with the way you worded that. Although the nmap utility can provide both of those answers, I’m not sure that’s what you meant. Technically nmap and ping are two different tools.