iOS 26 / 26.0.1 - No or slow DNS on cellular

Similar problem here.
Also the same configuration, but APN internet.telekom (IPv6) behaves the same as APN  internet.v4.telekom (IPv4).
 

On iPhone (iOS 26.4):
The first page load in Safari takes up to 10 seconds.
Subsequent page loads are fast.
First page loads in brave or edge are fast immediately.
First page loads in Safari with a manually created profile are fast, too.

On MacBook Air (MacOS 26.4):
Page loads are fast, no impact at all.

It seems that it's only slow in the browser-engine and in apps that use the browser-engine (e.g. NetNewsWire).
Apps itself load content fast.

wutti could you check if it's similar behaviour at your side ?

To compare the behaviour i just created a controld test-account.
I wanted to cross-check if it might conflict with iOS.
Using APN internet.telekom (IPv6).

On iPhone (iOS 26.4):
The first page load in Safari loads immediately.

The rest of the tests results are identically.

NextDNS Do we have a known issue here ?

I don't have this problem as I don't use IPv6. However, could it be because Safari uses Private Relay and there is some problem with Private Relay on IPv6. ControlD blocks iCloud Private Relay entirely. According to ControlD docs, they block the domains: mask .icloud. com and mask-h2 .icloud. com (NB: I've had to enter spaces to get around the forum restrictions imposed on me). Maybe try blocking these in NextDNS and see if it solves the problem. There is more information on Private Relay domains and NextDNS if you search for "yokoffing" Github NextDNS guide (sorry I can't link to it as I'm restricted in posting URLs).

Yes, Limit IP Tracking is deactivated  

I’ve now had a long and detailed conversation with a higher-level Apple Support department.  
They told me that there are some internal reports on this issue, but no detailed knowledge about it yet.  
We compared these statements with our own test results.

After that, we developed a plan for how to narrow down the errors.

In the meantime, I tested the whole thing once with a “new” device that was still running iOS 26.1.  
I installed a DoH profile and tested Safari with an IPv6 APN.  
There were no problems — normal speed.  
Then I updated to iOS 26.4 and tested again — still no problems, normal speed.

This suggests that the issue is related to the update, which occurs on 5 out of 6 existing devices.

After several additional tests according to the plan mentioned above, the following solution was found, which reproducibly fixes the problem on all 5 affected devices:

1. Completely reset Safari (Settings → Apps → Safari)  
   - Disable all extensions (in all profiles)  
   - Delete all (additionally created) profiles  
   - Clear history and website data (“All History” and “Close All Tabs”)  
   - Quit Safari (if not already done)  

2. Restart Safari once with the existing DoH profile  
   - Speed should now be normal  

3. Reconfigure Safari  
   - Re-enable desired extensions  
   - Recreate preferred profiles  

4. If “iCloud Private Relay” functions were disabled, they can be reactivated as needed:  
   - Settings → “Profile” → iCloud → “Private Relay” → enable  
   - Settings → Wi-Fi → “SSID” → “Limit IP Address Tracking” → enable  
   - Settings → Apps → Safari → “Hide IP Address” → enable for “Trackers and Websites” or “Trackers Only”  

If these changes don’t help, reset the network settings:  
   - Settings → General → Transfer or Reset iPhone → Reset → Network Settings  
(This has broader effects: Wi-Fi networks, Bluetooth connections, etc., need to be reconfigured.)

It’s likely that these issues are related to the update and the changes to “Happy Eyeballs” and the “WebKit engine.”

I wish you good luck!  
Everything’s working perfectly for me again.

Happy Easter!

This feels like it’s the same problem. I’ve been having with excessive latency on both of my iPhone 16 pros. First request always hangs - repeated requests - 3 or 4 retires - clears the latency and subsequent requests respond fine for a (indeterminate) time. 
 

I have the same issue whether I’m on my Wi-Fi network at home or on cellular.  However, it is very difficult to consistently reproduce because after repeated requests the latency clears up. So, troubleshooting becomes difficult, because what appears to work may have made a change or, it may have just triggered repeated requests which also cleared the latency.
 

At this point, I have performed the full reset of network settings, removed all Safari configs and extensions, and disabled private relay. That all seemed to work for a while, but today my latency has returned. Oddly, this isn’t seen on Opera or DuckDuckGo browser. 

FYI, I've been struggling with almost the exact same issues. In my case, I narrowed it down to 2.54 gigabytes of data, according to iPhone Storage settings. Nuking my website data reduced it 300 megabytes and now it went from loading pages after a force quit/cold start in 34 seconds to 1 second. I'll keep an eye on it to see if it stays that way, but I appreciate everyone's input!