Beginning on 7/30/2026 (version 732), users playing my game began reporting heavy FPS loss without us pushing any updates to the game. We began investigating and asking users for MicroProfiler logs, and it became clear that FastCluster::buildSkeleton was causing frame hitches in-game.
This issue does not appear to be isolated to a specific platform, as both console users and windows/mac users have reported experiencing the issue.
My setup (which I can reproduce the issue on) is:
Despite hours of troubleshooting specific models and removing static NPCs (targeting humanoids), I have not been able to reproduce this issue in Studio. However, I have gathered numerous MicroProfiler logs.
This issue is easily reproducible by playing my game and driving around the map. Tabbing out and then back in seems to kickstart the issue sometimes.
It also appears that another user on DevForum reported this same issue starting at the same time.
MicroProfiler Logs
I have attached 5 separately recorded MicroProfiler logs which all show the issue. PROFILER_LOGS.zip (9.5 MB)
I spend around 10 hours on this and in the end gave up. I couldn’t reproduce it a single time. But I did fix the issue itself, here is what I did:
In our game we have a corpse system, and for certain reasons we had to unparent accessories from character models when cloning a dead player’s character to create a corpse. We also had other meshes created on the client (bullet casings for example) that were parented to workspace.
So I followed advice from the Roblox Staff member. I found everything that was ever parented to workspace without a model during gameplay and just put it in models. So if your game ever parents anything to workspace, or a folder in the workspace, without that instance being a descendant of a model, that might be the cause.
Also, from my experience if they are static instances that don’t change hierarchy it’s fine if they’re not parented to a model and are in the workspace.
Important note: The system existed in our game for a long time and this issue never came up. I assume there was an update to the engine that caused this issue to appear seemingly out of nowhere.
