My non user avatar R15 Humanoid characters suddenly broke

Today at 3:42pm EST we got the first user report of a “jumping bug” in our game. It seems that our Humanoid based characters are having some really bad physics issues that were not present earlier in the day. The last update to our game was at 1:53am EST the same morning/last night, but none of the changed involved character controllers or models.

game link Apocalypse Rising 2 - Roblox

Our production, production testing build, and an older dev build all seem to have the same physics issues. One of our development builds (a few minor versions behind our production dev place) does not, and I cannot find a discrepancy between it and our current production build that explains the bug.

This video was recorded on our most up to date production build

Expected behavior

This video was recorded on the dev build that is working

This is currently breaking character movement for all players in my game.

Characters do not edit Humanoid.HipHeight at any time, and to jump we call Humanoid:ChangeState(Enum.HumanoidStateType.Jumping). The crouching animation is purely visual and does not adjust any humanoid or humanoidrootpart properties.

Collision groups all seem to be fine and set properly, collision rules don’t seem to be different across any of our builds.

Settings/properties on Workspace, StarterPlayer, and Player all match across all builds.

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Found a more specific repro:

In order to avoid animation collision issues, we use a custom head collider part that gets welded to the HumanoidRootPart. Disabling and enabling the joint between the HumanoidRootPart acts like an on/off switch for the bug. Switching from a Motor6D to Weld doesn’t make a difference.

This was never the case before today, and the working dev build currently uses the same collision system with no issues.

on the bugged build:

on the functioning build:

7:25 EST This appears to now be fixed?

Users are no longer reporting issues, and we can’t observe it happening anymore. We haven’t pushed any updates/fixes.

Probably was this flag that was toggled off to fix a similar bug:

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