I was assuming your server and Linux device were plugged in via Ethernet and your mobile devices were using WiFi. Now it sounds like your Linux system may be using the same access point.

It could be something as simple as your browser trying to send the address to a search engine instead of directly looking for the site.

When you’re trying to access it on mobile do you manually enter “http://” or “https://”? Those default to ports 80 and 443 respectively.

If you’re using nonstandard ports you may need something like “http://192.168.1.42:8080” to use http on port 8080 or any other nonstandard port.

Even if you are 100% sure your server is http or https try the other one to see if your error changes.

Some possibilities:

1. WiFi has host isolation is enabled
2. The network you’re connecting from is a guest wifi network
3. You configured a firewall rule to isolate WiFi from LAN
4. VLAN is enabled

I’m using Synology Photos + Syno Photo Frame & a custom bash script to rotate photo albums on a Raspberry Pi 5.

The above is connected to a 4k monitor with USB C power delivery so it can all be toggled on/off by a standard switched outlet.