Some devices are missing in the LAN scanner results

There can be various reasons for this.

First, this typically happens with devices in power-save mode, such as phones, tablets, or notebooks, which try to preserve as much power as possible by disabling wifi reception for short periods of time and don't respond to the probes sent by Network Analyzer. Such devices sometimes appear in the results and sometimes don't.

Second, your router may have "wireless isolation" enabled (various manufacturers use different terms for this feature). When this feature is enabled, individual devices don't see each other. Such a setting is often used in public wifi networks such as hotels or airports for security/privacy reasons. It is usually possible to disable this feature in the router's settings.

Finally, wifi routers sometimes isolate devices connected to the 2.4GHz network from devices connected to the 5GHz network, so devices connected to the 2.4GHz network don't see devices connected to the 5GHz network, and vice versa. Again, this can usually be configured in the router's settings.