Hilariously I've spent hours troubleshooting why my Pi running Pi-hole is intermittently inaccessible from my iPhone, despite being able to connect to the Pi from other machines. I still have no clue why. Last night I finally captured a tcpdump so maybe I can see what is happening (the Pi is indeed receiving packets from the iPhone), but it's totally inexplicable. The other Pi I have always hooked up (music player for my speakers) has a bash script that runs every 5 min with cron, to ping the LAN router and restart networking if it can't ping it. Why? Because after a while the Pi would randomly drop off the network and become inaccessible. Countless stuff online gives various troubleshooting which never made any difference, until I employed my hackish "check the network every 5min" which has completely "solved" the problem. Unfortunately this didn't "solve" the problem for the Pi running Pi-hole, sadly.