NPCs Caused Server Crashes now

General Issues and Bug Reporting
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1

Summary

Starting immediately after the Fortnite 39.00 update (Nov 29–30 2025), all of my AI-heavy islands that use custom npc_behavior scripts combined with NPC Spawner / Guard Spawner devices began experiencing extreme server instability. These islands were 100% stable for over a month prior to 39.00 with no Verse changes on my side.

Since 39.00, these islands now produce 20–100 server crashes per day, affecting live players in public matches. This regression impacts multiple islands, multiple spawners, and multiple behavior implementations, all of which previously ran flawlessly.

This appears to be a core AI / Scene Graph / NPC component regression introduced in 39.00.

When the Issue Started

Approximately 24–36 hours after v39.00 went live, every island using custom NPC logic started producing:

Server crashes

NPC freezes / desyncs

Hard AI shutdown during runtime

Public matches collapsing with identical error types

No code was changed during this window. Maps that had been stable for 30+ days immediately started failing.

Number of Maps Affected

Hunt the Spino

Hunt the Santa

Hunt the T-Rex

Additional prototype islands using the same AI framework

All show identical problems starting after 39.00.

Frequency

100–1500 server crashes per day per map, verified across:

Public matches

Long private sessions

Dedicated test runs

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

AI

Steps to Reproduce

Have Custom NPC code in your project

Expected Result

Servers not crash

Observed Result

NPCs work but servers crash now

Platform(s)

All

2

Can also confirm major instability with NPCs after 39.00

1 Like
3

I have a ‘test project’ with a single npc, single player, and almost no assets. I’ve noticed significant lag when I go to test. A project I have with 10 npcs just flat-out crashed when testing (video card out of ram), although it ran fine last week.

4

Absolutely brutal. My entire brand is built on NPCs. I appreciate you confirming this.

5

Does the message “session may end unexpectedly” appear? Because after the patch, someone reported to me that after playing my map for a while, this message appeared and then it crashed(back to lobby) (this never happened before v39).

1 Like
6

Yes - that sounds about right - i received similar message. Note that other messages are displayed too.

1 Like
7

but this happens only with npcs or also with guard spawners, because in my map I have both(npcs have no verse behavior, only Character Definitions)

9

Here is my twitter thread with a video on it

12

Can confirm instability as well.

Players reported these things:

”It was quite laggy yesterday and the guards spawning and despawning has been confusing to say the least. Sometimes they even showed up as Defaults. Weird.”

”Had it a few times where the guards didn’t dissappear after dying,also they sometime spawned in invisible…could only see their red dots on the mini map and their floating weapons”

I will try to gather video proof of that.

13

FORT-1026915 is ‘Closed’ as ‘Fixed’. The issue will be addressed in 39.00.

1 Like
14

Was just going to post confirming this issue may still be occurring, just to see that this was an issue that’s going to be fixed! :heart:

15

After the latest update 39.10 the issue still persists and it seems that’s I got many reports of the lag being still present in my map(which uses the NPCs)

1 Like
16

Same here on my end, even with 4 NPCs it gets pretty bad after a while

17

Nevermind - issue was with my code performing untracked subscriptions! Things have been smooth but I may come back with more updates.

1 Like
18

Hey, mind sharing those untracked subscriptions? Thank I’d love to see what I can do fix it for now!

19

Still seems to happen in my map as well. Will try to gather more informations on this

20

It was just a few endlessly subscribing events that occurred when NPCs got within range that I had to do to workaround interactables being broken; issues have kept popping up since then though :smiling_face_with_tear:

1 Like
21

@Flak could you get someone to look into this? The issue still seems to happen even though it’s marked as fixed.

2 Likes
22

This issue is still happening, it is heavily affecting the performance of maps that uses the NPCs

1 Like