Entity pathfinding paths do not appear with 1.21.9 debug flag enabled

[joshuaprince]

Expected behavior

1.21.9 added -DMC_DEBUG_PATHFINDING. It shows pathfinding paths to clients when connected to a Vanilla server.

Observed/Actual behavior

On a Paper server, pathfinding paths do not show up at all.

Steps/models to reproduce

1. In client, enable debug JVM flags -DMC_DEBUG_ENABLED -DMC_DEBUG_PATHFINDING (these flags don't seem to be required in the vanilla server to show clients paths, but adding them on the Paper server does not fix it)
2. Join vanilla server
3. Watch any mob moving to confirm paths appear
4. Swap vanilla JAR for Paper
5. Watch any mob moving, paths do not appear

Plugin and Datapack List

No plugins or datapacks installed.

Paper version

ver
[21:41:23 INFO]: Checking version, please wait...
[21:41:23 INFO]: This server is running Paper version 1.21.9-53-main@4dcd837 (2025-10-05T22:42:14Z) (Implementing API version 1.21.9-R0.1-SNAPSHOT)
You are running the latest version
Previous version: 1.21.9-51-b63dc92 (MC: 1.21.9)

Other

No response

[Lulu13022002]

Caused by this patch: https://github.com/PaperMC/Paper/blob/main/paper-server/patches/features/0013-Optimize-Pathfinder-Remove-Streams-Optimized-collect.patch#L56 not sure if it was intended or not seeing that comment