(server authority) crash due to "RBXCRASH: assembly primitive is null"

Bug Reports Engine Bugs
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1

While attempting to constrain a part to a players hand via an AnimationConstraint I ran into inconsistent crashes on attaching/deattaching said part. I am trying to use this system to pick up a tool and then be able to throw it. My process is as follows:

(on grab)
set AnimationConstraint Attachment0 to Part player is grabbing
Set Part to massless
Set Part to cancollide false

(on throw)
set AnimationConstraint Attachment0 to nil
Set Part to not massless
Set Part to cancollide true
Set Part AssemblyLinearVelocity to simulate throw

All of these steps are handled in BindToSimulation and the game still crashes on what seems to be setting Attachment0. It seems a bit arbitrary wether the crash occurs, sometimes on first grab it happens while other times I can pick up and throw it 4-5 times before it crashes.

I have experienced this bug in both studio and live servers. I have been able to repro it on both a windows 11 PC with an Intel Core Ultra 9 275HX @ 2.7 GHz, 64 GB, NVIDIA GeForce RTX 5060 and an iphone 13.

Here is a repro file and steps:
CrashRepro.rbxl (61.5 KB)
play uploaded file and hit E repeatedly within 15 studs of red part. the faster you hit it the more consistently the crash seems to happen.

A private message is associated with this bug report

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2

bump. I have tested to see if WeldConstraint objects would work and they also crash. Motor6D and legacy Welds are also not viable as you cant set C0/C1 in BindToSimulation.

I cannot work on the core mechanic of my game further until I get this working. Until the crash is fixed the only way around it I can think of is setting the parts position every RenderStepped to mimick what it would be if it was constrained via an AnimationConstraint. This is obviously super hacky and Iā€™d like to not go down this route.

3

I can confirm this crashes the game on both studio and live environments.

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4

Thx for the report. We are investigating. Sry for the trouble!

2 Likes
5

This issue should be fixed now. Please give it a try now to confirm this is the case. Let me know if you have any problems. Thanks.

2 Likes
6

looks to be fixed on my end. thank you!

1 Like
7

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