I’m trying to find out whether anyone else can reproduce this.
My setup:
• Local AdGuard Home on Raspberry Pi
• Home Wi-Fi uses a manually configured local DNS server (192.168.1.x)
• Cellular uses an iOS DNS-over-HTTPS configuration profile
• Private Relay is OFF
After updating to iOS 27 Developer Beta 3 (now also reproduced on the Public Beta branch), I started seeing a strange issue.
After the phone sits idle for several hours (typically overnight), DNS-based filtering suddenly stops working.
Symptoms:
• Ads that were previously blocked (e.g. Google/DoubleClick) start loading.
• Internet connectivity still works normally.
• My AdGuard server itself is healthy.
• The same DNS server works perfectly through Tailscale.
Initially I suspected:
• Cloudflare Tunnel
• AdGuard Home
• IPv6
• the DNS profile itself
But none of those fully explained the behavior.
Then I noticed something interesting.
Around the time the issue occurs, iOS sometimes displays:
“Connectivity Assist - iPhone is using cellular data in addition to Wi-Fi for a more reliable internet connection.”
After disabling Connectivity Assist, I have not been able to reproduce the issue so far, even after leaving the phone idle overnight.
I’m not claiming Connectivity Assist is the root cause, but it currently looks like a strong correlation.
Questions:
1) Has anyone else seen DNS settings seemingly being ignored after long idle?
2) Does disabling Connectivity Assist make any difference for you?
3) Has anyone updated to Developer Beta 4 yet and noticed if this is still happening, or did Apple tweak the Connectivity Assist / fallback behavior?
I’d appreciate any confirmations or alternative explanations.
TL;DR: On iOS 27 Developer Beta, after several hours of idle on home Wi-Fi, DNS filtering (AdGuard Home / Pi-hole) stops working and ads load. Disabling Connectivity Assist (Settings > Wi-Fi) seems to fix it. Looking for DB4 users to confirm if this DNS bypass/leak is still happening.