Blazor Web App on IIS: Safari iOS 18.2.1 Rejoins Slowly (10-30s Delay)

[nieuwveen]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When running a Blazor Web App with Interactive Render (Global mode) on a Windows Server 2022 (IIS, WebSockets enabled, SSL configured), the app experiences a slow rejoining process (10-30 seconds) when switching back to Safari on an iPhone 15 Pro (iOS 18.2.1) after the browser has been in the background for a few seconds.

This delay occurs when Safari suspends the WebSocket connection while the app is in the background. Upon returning, Blazor attempts to restore the connection and rejoin the same session, but the process is unexpectedly slow. Instead of an instant reconnection (expected within 1-2 seconds), the app takes anywhere from 10 to 30 seconds to rejoin, making the user experience sluggish and unresponsive.

Expected Behavior

The expected behavior is that the session should reconnect instantly or within 1-2 seconds. However, it takes 10-30 seconds, making the app feel unresponsive.

This issue does not seem to occur on other browsers (IOS Edge, or using a webview (PWAbuilder.com))

Steps To Reproduce

Video ->
https://github.com/user-attachments/assets/8e13ca3f-98d7-4275-97f2-6cf0a8b43964

Steps to Reproduce
Create a new Blazor Web App .Net9 (dotnet new blazor -n MyApp)
Choose interactive render, global
Modify the Main Page
Add an field to track session state
Publish the App to IIS on a Windows Server 2022
Ensure WebSockets is enabled in IIS
Add an SSL certificate
Open the app in Safari on iPhone 15 Pro (iOS 18.2.1)
Enter some text in the input box
Switch to another app for ~10 seconds
Switch back to Safari
Notice "Rejoining server…" appears and takes 10-30 seconds
Check if the same circuit/session is used

Exceptions (if any)

No response

.NET Version

9.0.102

Anything else?

No response

[javiercn]

@nieuwveen thanks for contacting us.

Is the session able to resume after the disconnection or does the page refresh and a new session gets started?

[nieuwveen]

@javiercn Yes, the session resumes after disconnect
(its visible in the video, @ sec 30, the same text input is still there)

[nieuwveen]

@javiercn
I created a screenshot of the safari dev tools on my mac, the negotiate process takes 47 secondes, then it resumes the same session.

[danroth27]

@nieuwveen Did this only start happening recently? Or has this behavior always been this way for your app?

[danroth27]

Potentially related to #48724

[nieuwveen]

@nieuwveen Did this only start happening recently? Or has this behavior always been this way for your app?

We’re not entirely sure when it happened, but after upgrading to .NET 9, we removed our reconnect window because the new version looks so nice. Along with that, we also removed our reconnect logic. Previously, when the connection dropped, our code would initiate a ping to a specific endpoint. If the ping succeeded, we performed a hard reload using document.location.reload.

We like the new reconnect window and also that it resumes the same session.

Do you have any idea why resuming the session takes over 30 seconds?
We know that Safari disconnects the socket connection, and that's something we can’t change.
(And that should be okay because it’s energy efficient.)

For now, I can add some custom reconnect logic: if it’s Safari, then skip the slow resume.
For us, this is the only important improvement, as we have 4,000+ mobile users daily.