[Major] ~50% of players receive a Network Error after successful Matchmaking

General Issues and Bug Reporting
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1

Summary

A very large number of players are unable to join our map because of a Network Connection Error. The reason is unknown and we have no way to investigate the root cause on our own.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Matchmaking

Steps to Reproduce

Reproduction steps are unclear. It appears to happen more commonly on consoles, but not exclusively and not consistently.

Our game has a large project size of 82% and download size of 330 MB. However, players fail to connect after having successfully Downloaded the map.

Players who fail to connect can often succeed when trying again hours later (although a very small % bother trying again). Immediate re-tries fail more often than not, even after restarting the game and even console.

When previously blocked players do get in they experience no noticeable lag. Client performance is perfectly fine, sitting at 1.9% Missed Frames overall.

Expected Result

Substantially less connection errors. Players should make it into the game.

Observed Result

With the data at our disposal, we estimate about half of the players who attempt to get into our map are failing to complete the “Connecting” stage after successful matchmaking.

Looking at Analytic data from July 16, there were 25,460 Successful Matchmaking results (only 288 failures). In the same time period there were only 13,826 Plays (54%), and an analytic_device triggered on first player interaction concurs with this concerningly low number of Plays per Matchmaking Success.

When sitting in a public server, we’re able to observe players appearing on the Team HUD with a health and shield of 0/0. Some players manage to fully load, but failing players never have their character spawn in game, then disappear from the Team HUD (See “In Game Perspective” video).

From reports of players who are unable to join and our own testing, one of the following 3 errors appears when Connecting fails:

  • Client failed to register with server. Please restart Fortnite
  • Network Connection Lost
  • We failed to establish a connection to the server; FailedToConnect

This result seems tied to this specific map as we have not/are not experiencing the same issue on other maps. However, we have no tool nor logs at our disposal to debug this further.

Platform(s)

All

Island Code

1465-4940-2309

Video

Player Perspective - https://www.youtube.com/watch?v=47auTBuqh28
This is just one of the three errors players are receiving after successful matchmaking.

In Game Perspective - https://www.youtube.com/watch?v=iWAxQy4yrnw
Notice players appearing on Team HUD in the top right, but never physically appearing (spawn pads are straight ahead).

2

FORT-938046 has been created and its status is ‘Unconfirmed’. This is now in a queue to be reproduced and confirmed.

3

works on Samsung Android phone and Switch 1
very slow on PC
in fortnite settings set network ping times on/ visible in UK GMT 2300 10ms most time, phone
NS1 <20 ms

laptop win 11 <40ms

Do you get queue → full in PC Fn logs

4

After some more attempts, we got a clean log file of at least one of the three error messages on PC (“Network Connection Lost”). Here’s a video and full game log of this error:
https://www.youtube.com/watch?v=ywsTJM5Oj2Q
FortniteGame-ErrorJoining.log (4.0 MB)

Comparing this log to a working game join log yields this specific error:

LogNet: NMT_CloseReason: (Server Disconnect Reasons) 20.185.51.181:9045
LogNet:  - HostClosedConnection
LogNet: UNetConnection::SendCloseReason:
LogNet:  - Result=FailureReceived, ErrorContext="FailureReceived"
LogNet: Error: UEngine::BroadcastNetworkFailure: FailureType = FailureReceived, ErrorString = DataStreamChannel failed to write data., Driver = Name:GameNetDriver Def:GameNetDriver IpNetDriver_2147482636
LogNet: Warning: Network Failure: GameNetDriver[FailureReceived]: DataStreamChannel failed to write data.
LogNet: NetworkFailure: FailureReceived, Error: 'DataStreamChannel failed to write data.'
LogFort: [HandleDisconnectInternal] bHandlingDisconnect: false
LogParty: Verbose: UFortPartyMember::HandleLocationChanged for [Jacobg1998] from [InGame] to [ReturningToFrontEnd] in [None]
LogFort: [3af2] New Session Started - PlayerLeftVoiceGameChannel flag was reset
LogParty: Verbose: UpdateChangeCallbacks: Getting Team Member Info for [Jacobg1998] Id [MCP:de0dff7dd1184545a25d97a8c8227c9a].
LogParty: Verbose: [Jacobg1998] Id [MCP:de0dff7dd1184545a25d97a8c8227c9a] team member data updated, team [MAX] at index [0] in [Jacobg1998]'s game.
LogMatchmakingUtility: [HandlePartyMemberLocationChanged called] MCP:de0dff7dd1184545a25d97a8c8227c9a, Party (V2:5d90aa0611d749cea7f34ad4ac8cafb7) location changed to: ReturningToFrontEnd None
LogNet: UNetConnection::Close: [UNetConnection] RemoteAddr: 20.185.51.181:9045, Name: IpConnection_2147482636, Driver: Name:GameNetDriver Def:GameNetDriver IpNetDriver_2147482636, IsServer: NO, PC: Athena_PlayerController_C_2147482642, Owner: Athena_PlayerController_C_2147482642, UniqueId: MCP:de0dff7dd1184545a25d97a8c8227c9a, Channels: 3, Time: 2025.07.17-18.05.59, TimeSinceTickDispatch: 0.035244, TimeSinceRecv: 0.001937, TimeSinceTickFlush: 0.622237, TimeSinceSend: 0.622186
LogNet: UNetConnection::SendCloseReason:
LogNet:  - Result=FailureReceived, ErrorContext="FailureReceived"
LogNet: UChannel::Close: Sending CloseBunch. ChIndex == 0. Name: [UChannel] ChIndex: 0, Closing: 0 [UNetConnection] RemoteAddr: 20.185.51.181:9045, Name: IpConnection_2147482636, Driver: Name:GameNetDriver Def:GameNetDriver IpNetDriver_2147482636, IsServer: NO, PC: Athena_PlayerController_C_2147482642, Owner: Athena_PlayerController_C_2147482642, UniqueId: MCP:de0dff7dd1184545a25d97a8c8227c9a
LogNet: Error: UEngine::BroadcastNetworkFailure: FailureType = ConnectionLost, ErrorString = Your connection to the host has been lost., Driver = Name:GameNetDriver Def:GameNetDriver IpNetDriver_2147482636