Turned on WPA3 and a few older devices went quiet? Mixed mode and the handshake it uses is usually why. Here's the mechanism behind it.

Same network, same room, and the app still says it can't find the device. Blocked mDNS and multicast traffic is usually why. Here's the fix.

AP isolation blocks devices on the same Wi-Fi from talking to each other, even with internet working fine. Here's how to check it, and the trade-off.