Mover based NPCs triggering "Invalid interpolation frames" SystemFault in NetworkPrediction

Development Programming & Scripting Multiplayer & Networking
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It would seem that bandwidth throttling in combination wtih more than a trivial number of Mover actors is enough to trigger the error logs about Invalid interpolation frames. The throttling seems to cause the server to cut back on updates for some NPC actors to the client, then those actors then fall behind enough that interpolation fails.

Note that:

* Turning on net.disableBandwidthThrottling prevents these logs.

* Switching Simulated Proxy Network LOD to ForwardPredict instead of Interpolate prevents these logs. But this is directly against the recommendations of the Mover Examples project.

* I am running with Network Emulation disabled, but expect that turning it on would just make this more likely to hit.

I’m not sure if anything bad is happening here other than the spammy and slow logs.

Is there some way I need to configure NPCs’ Mover components differently? Is there some other configuration needed here? Should Mover not be used with NPCs? Is it actually fine that it’s hitting this and there’s something I can do to shut down this log for these NPCs? I would expect in these cases that it would be fine for my NPCs, especially those further away, to not worry about this interpolation. But “System Fault” sounds like a big deal and I’m not sure all the implications.

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Steps to Reproduce

  • Create a new project with Mover & Mover Examples plugin
  • Load up L_CharacterMovementBasics from the examples plugin
  • Setup project settings based on mover examples recommendations
  • Duplicate the ScriptedMannyPawn that’s in the level until you have 16 of them (exact number uncertain but this was easily enough for me to see it)
  • Run the game in PIE as Client
  • Note the repeated logs like: LogNetworkPrediction: SystemFault: Invalid interpolation frames. Copying old content forward. LastWrittenFrame: 230. ToFrame: 231
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Hi,

Thank you for the report!

I can reproduce the issue you’ve described here, but to double check, are you seeing any problems with the movement of the NPCs when this fault is repeatedly getting logged?

Mover is intended to be used for both player controlled characters and NPCs. However, I don’t believe there’s any easy way to configure the Network Prediction Plugin differently for different types of characters.

I’m also not sure there’s any way to hide that log, other than reducing the verbosity of the LogNetworkPrediction category below “Log”.

Thanks,

Alex

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We have seen a bit of movement weirdness, especially with our NPCs not moving for periods, but at this time we don’t have reason to believe this is the cause. The intensity of the log led me to believe there could be some relation. Turning the log verbosity down isn’t a great option because if this happens to a player character, I’m gonna want to hear about it. Having some ability to tell a particular actor type that it is allowed to silently fall back this way would be useful. Or even notice that it’s been deprioritized for bandwidth and just not even try.

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Hi,

Given that there doesn’t seem to be a correlation between these logs lines and any movement issues, it does seem like the severity of the message could at least be reduced in order to avoid it bloating the logs. I also agree that having further control over how Mover/NPP is configured for different character types would be helpful.

I’ve raised both of these with the team for further consideration.

Thanks,

Alex