FUdpSocketBuilder errors causing frame rate drops but no networking in project

Development Programming & Scripting Multiplayer & Networking
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I’m having a strange issue where my frame rate is tanking every second or so and the profiler is pointing to FUdpSocketBuilder as the culprit. I’m not doing any networking in this project so this is a weird thing to have come up out of the blue, it just started happening the other day, but went away after a while and now it’s back. It seems to have popped up around the time I added the Steam online subsystem plugin. I was going to play around with using it for networking but decided that the project needed to advance before I could work on network play. I removed the plugin to see if it was the issue but I’m still getting the same problem. I should also point out that this issue is happening in the editor as well as during play.

Here are the errors coming up in the session front end:

FUdpSocketBuilder: Failed to subscribe UdpMessageMulticastSocket to multicast group 230.0.0.1 on interface 0.0.0.0
2020.07.06-23.29.36 [DEVELOPER1-22740] 00328.490: FUdpSocketBuilder: Failed to create and initialize socket UdpMessageMulticastSocket (last error: 0)
2020.07.06-23.29.36 [DEVELOPER1-22740] 00328.490: LogUdpMessaging: StartTransport failed to create multicast socket on 0.0.0.0:0, joined to 230.0.0.1:6666 with TTL 1
2020.07.06-23.29.36 [DEVELOPER1-22740] 00328.506: LogUdpMessaging: UDP messaging encountered an error. Auto repair routine started for reinitialization

These errors are coming up over and over every few seconds. Like I said I’m not doing any networking that I know of (this project is all blueprints right now while I work on prototyping mechanics) so I’m not even sure where to look to find the source of the issue. Anyone have any ideas?

Edit: Some things that I’ve tried

  • Creating a new project and migrating assets to new project (same issue)
  • Cleaning/Rebuilding the source code (no change)
  • Creating a new project in a lower version and migrating assets (version 4.24, same issue)
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For me it started after windows update, firewall related I think. Fixed by fiddling with windows defender settings.

Btw you can get rid of it by disabling project settings>plugins>udp messaging>enable transport but that’s not a fix

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For anyone else running in to this. I use NordVPN and had my Dedicated IP set to OpenVPN (UDP). Changed it to TCP and the errors stopped in the UE4 editor.

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It is an engine error, maybe based on some cache, here my theory and solution:

If you opened the project before, let’s say, connected to Wifi, and then you disconnect wifi and use cable, it will still try to connect though that same network adapter. Same with VPNs (That are virtual network adapters).

So my workaround is to disable the network adaptar that is causing this.
Control Panel → Network and Internet → Right click and disable the one is causing it (try and error) but for sure is one that is not connected right now.

Hope this helps someone.

5 Likes
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For me it stops after I connect to my workplace VPN. I set up SVN version control in engine and this error message begins pop up after VPN connection drops.

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Thank you. I fixed the issue, 1st desabling then enabling back the Ethernet adapter.

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Thanks - was an internet issue having to do with wifi / ethernet needing to be reset.

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This solved it for me, thank you for posting that!