Hi everyone,
I’m running into a issue with Unreal Engine’s Iris replication system. My dedicated server crashes consistently when exactly 128 players are connected. As soon as a new connection is attempted, the server throws an error and shuts down.
Here’s the relevant log output:
[2025.09.26-09.11.43:638][ 38]LogIris: Error: UReplicationSystem::AddConnection called with a bad connection Id: 128. Max connection count: 128.[2025.09.26-09.11.43:638][ 38]LogOutputDevice: Warning:
Script Stack (0 frames) :
Assertion failed: Index < BitCount [File:Runtime/Net/Core/Public\Net/Core/NetBitArray.h] [Line: 697]
[2025.09.26-09.11.43:648][ 38]LogCore: Error: appError called: Assertion failed: Index < BitCount [File:Runtime/Net/Core/Public\Net/Core/NetBitArray.h] [Line: 697]
[2025.09.26-09.11.43:668][ 38]LogCore: Assertion failed: Index < BitCount [File:Runtime/Net/Core/Public\Net/Core/NetBitArray.h] [Line: 697]
0x0000000004f5e519 UnrealEvaluation2025Server!FDebug::CheckVerifyFailedImpl2(char const*, char const*, int, char16_t const*, …) [C:/UnrealEngine/Engine/Source/./Runtime/Core/Private/Misc/AssertionMacros.cpp:724]0x00000000080b04d3 UnrealEvaluation2025Server!UReplicationSystem::SetConnectionUserData(unsigned int, UObject*) [C:/UnrealEngine/Engine/Source/Runtime/Net/Core/Public/Net/Core/NetBitArray.h:697]0x000000000b12■■■0 UnrealEvaluation2025Server!UNetConnection::InitBase(UNetDriver*, FSocket*, FURL const&, EConnectionState, int, int) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/NetConnection.cpp:624]0x000000000e56d138 UnrealEvaluation2025Server!UIpConnection::InitBase(UNetDriver*, FSocket*, FURL const&, EConnectionState, int, int) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpConnection.cpp:113]0x000000000e56df96 UnrealEvaluation2025Server!UIpConnection::InitRemoteConnection(UNetDriver*, FSocket*, FURL const&, FInternetAddr const&, EConnectionState, int, int) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpConnection.cpp:159]0x000000000e575e98 UnrealEvaluation2025Server!UIpNetDriver::ProcessConnectionlessPacket(FReceivedPacketView&, FPacketBufferView const&) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpNetDriver.cpp:1451]0x000000000e574e15 UnrealEvaluation2025Server!UIpNetDriver::TickDispatch(float) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpNetDriver.cpp:1270]0x000000000b1626dd UnrealEvaluation2025Server!UNetDriver::InternalTickDispatch(float) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/NetDriver.cpp:2198]0x000000000b19c6d2 UnrealEvaluation2025Server!TBaseUObjectMethodDelegateInstance<false, UNetDriver, void (float), FDefaultDelegateUserPolicy>::ExecuteIfSafe(float) const [C:/UnrealEngine/Engine/Source/Runtime/Core/Public/Templates/Invoke.h:66]0x0000000005d8a4b4 UnrealEvaluation2025Server!void TMulticastDelegateBase::Broadcast<IBaseDelegateInstance<void (float), FDefaultDelegateUserPolicy>, float>(float) const [C:/UnrealEngine/Engine/Source/Runtime/Core/Public/Delegates/MulticastDelegateBase.h:258]0x000000000b03f9b2 UnrealEvaluation2025Server!UWorld::Tick(ELevelTick, float) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/LevelTick.cpp:1335]0x000000000ad8011e UnrealEvaluation2025Server!UGameEngine::Tick(float, bool) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/GameEngine.cpp:1875]0x000000000c1f3a26 UnrealEvaluation2025Server!FEngineLoop::Tick() [C:/UnrealEngine/Engine/Source/./Runtime/Launch/Private/LaunchEngineLoop.cpp:5619]0x000000000c1f990a UnrealEvaluation2025Server!GuardedMain(char16_t const*) [C:/UnrealEngine/Engine/Source/./Runtime/Launch/Private/Launch.cpp:60]0x000000000c143695 UnrealEvaluation2025Server!CommonUnixMain(int, char**, int ()(char16_t const), void (*)()) [C:/UnrealEngine/Engine/Source/./Runtime/Unix/UnixCommonStartup/Private/UnixCommonStartup.cpp:323]0x00007fa3c427924a libc.so.6!UnknownFunction(0x27249)0x00007fa3c4279305 libc.so.6!__libc_start_main(+0x84)0x0000000004c8602a UnrealEvaluation2025Server!_start [/srv/flo/LinuxServer/UnrealEvaluation2025/Binaries/Linux/UnrealEvaluation2025Server:-1]
0x0000000004f5e519 UnrealEvaluation2025Server!FDebug::CheckVerifyFailedImpl2(char const*, char const*, int, char16_t const*, …) [C:/UnrealEngine/Engine/Source/./Runtime/Core/Private/Misc/AssertionMacros.cpp:724]0x00000000080b04d3 UnrealEvaluation2025Server!UReplicationSystem::SetConnectionUserData(unsigned int, UObject*) [C:/UnrealEngine/Engine/Source/Runtime/Net/Core/Public/Net/Core/NetBitArray.h:697]0x000000000b12■■■0 UnrealEvaluation2025Server!UNetConnection::InitBase(UNetDriver*, FSocket*, FURL const&, EConnectionState, int, int) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/NetConnection.cpp:624]0x000000000e56d138 UnrealEvaluation2025Server!UIpConnection::InitBase(UNetDriver*, FSocket*, FURL const&, EConnectionState, int, int) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpConnection.cpp:113]0x000000000e56df96 UnrealEvaluation2025Server!UIpConnection::InitRemoteConnection(UNetDriver*, FSocket*, FURL const&, FInternetAddr const&, EConnectionState, int, int) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpConnection.cpp:159]0x000000000e575e98 UnrealEvaluation2025Server!UIpNetDriver::ProcessConnectionlessPacket(FReceivedPacketView&, FPacketBufferView const&) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpNetDriver.cpp:1451]0x000000000e574e15 UnrealEvaluation2025Server!UIpNetDriver::TickDispatch(float) [C:/UnrealEngine/Engine/Source/./../Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Private/IpNetDriver.cpp:1270]0x000000000b1626dd UnrealEvaluation2025Server!UNetDriver::InternalTickDispatch(float) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/NetDriver.cpp:2198]0x000000000b19c6d2 UnrealEvaluation2025Server!TBaseUObjectMethodDelegateInstance<false, UNetDriver, void (float), FDefaultDelegateUserPolicy>::ExecuteIfSafe(float) const [C:/UnrealEngine/Engine/Source/Runtime/Core/Public/Templates/Invoke.h:66]0x0000000005d8a4b4 UnrealEvaluation2025Server!void TMulticastDelegateBase::Broadcast<IBaseDelegateInstance<void (float), FDefaultDelegateUserPolicy>, float>(float) const [C:/UnrealEngine/Engine/Source/Runtime/Core/Public/Delegates/MulticastDelegateBase.h:258]0x000000000b03f9b2 UnrealEvaluation2025Server!UWorld::Tick(ELevelTick, float) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/LevelTick.cpp:1335]0x000000000ad8011e UnrealEvaluation2025Server!UGameEngine::Tick(float, bool) [C:/UnrealEngine/Engine/Source/./Runtime/Engine/Private/GameEngine.cpp:1875]0x000000000c1f3a26 UnrealEvaluation2025Server!FEngineLoop::Tick() [C:/UnrealEngine/Engine/Source/./Runtime/Launch/Private/LaunchEngineLoop.cpp:5619]0x000000000c1f990a UnrealEvaluation2025Server!GuardedMain(char16_t const*) [C:/UnrealEngine/Engine/Source/./Runtime/Launch/Private/Launch.cpp:60]0x000000000c143695 UnrealEvaluation2025Server!CommonUnixMain(int, char**, int ()(char16_t const), void (*)()) [C:/UnrealEngine/Engine/Source/./Runtime/Unix/UnixCommonStartup/Private/UnixCommonStartup.cpp:323]0x00007fa3c427924a libc.so.6!UnknownFunction(0x27249)0x00007fa3c4279305 libc.so.6!__libc_start_main(+0x84)0x0000000004c8602a UnrealEvaluation2025Server!_start [/srv/flo/LinuxServer/UnrealEvaluation2025/Binaries/Linux/UnrealEvaluation2025Server:-1]
[2025.09.26-09.11.43:669][ 38]LogExit: Executing StaticShutdownAfterErrorEngine crash handling finished; re-raising signal 11 for the default handler. Good bye.Segmentation fault (core dumped)
So far it looks like Iris hard-caps connections at 127. When the 128th player tries to join, the replication system tries to assign a connection ID outside the allowed range, which immediately triggers the assertion.
I’ve already checked my DefaultEngine.ini and set higher values for MaxPlayers, but that doesn’t solve the crash – it still happens right at 128.
[/Script/OnlineSubsystemUtils.IpNetDriver]
MaxPortCountToTry=1
NetServerMaxTickRate=30
MaxPlayers=1024
Is there a way to increase the maximum number of connections beyond 128?
Any guidance would be greatly appreciated. Thanks!