I had the same issue and found that setting up to the homeassistant.local instead of the IP address worked. Not sure if that was a fluke though…
I do not think it is networking, they rather mess with webkit engine. More an more issues arise as they upgrade Safari. Many people on this forum reported issue when connecting from Safari using local IP:8123 connection (page not loading or requires several retries to reload to get content), using mDNS or external URL solves this. This happens only with Safari or apps using webkit. Other browsers (well, on Mac) do not have this problem.
Other issues are related to lading animated SVG, or the most recent: when loading HA from App all content is displayed properly, but when loading it as web page directly into Safari, some menu items are missing (Settings, Notifications, User Profile). The last one only on Mobile Safari. These issues started earlier, starting iOS26.
I’ve just done the same and that fixes it for me.
Set internal url on the app to
http://homeassistant.local:8123/
This works for me too, both on IOS 26.4 build 23E5223f and iPadOS 26.4 build 23E5218e
I have never been able to resolve internally with http://homeassistant.local:8123 i have always used http://192.168.x.x:8123 and now it stopped working internally through the app. Any ideas what can i do in that case
I’ve read elsewhere it is especially common if you have multiple APs with the same SSID (as I do with a Synology MESH WiFi.).
if true, this doesn’t make sense unless home assistant is somewhat using mdns when using the ip address and your AP have mdns disable.
I have mdns enabled and working on my two unifi AP and local network… so it must be something else.
I can confirm not only did it work for Carlhward, but also for me. After changing the internal URL from ip to mDNS address connecting to the server is done like before
Just updated to latest iOS Beta 26.4 and it seems to have fixed this issue 
confirmed. working for me too on my iphone et ipad running the latest beta. but not sure if this is related to the latest beta OS or the latest testflight home assistant build.
Same here 
I have a slightly different solve in that if I turn on my VPN (link to home network) it works ok. If I turn VPN off I see similar issues to reported here, unable to connect.
I’m not on any Beta versions of iOS, 26.3.1.
I just Updated from IOS18 now to IOS 26.4 and recognised extreme poor App Connection (Connection lost After app toggle) and data loading on Home Assitant App and also some Other Apps for local WIFI devices.
No issue when connected from external by VPN. Then always very fast data load for local wifi devices.
So I deleted on The iPhone the Wifi Connection Access (ignore) and created a new WIFI Connection and Manually Passwort Input.
Now it works Perfect and all data from local devices are losging very fast, same as before iOS Update.