Summary
An unknown bug affecting HingeConstraint is breaking both my games and various other games that use HingeConstraint in a similar way. The games involve trains and the bug is causing one car in the trains to disappear. This bug seems to occur randomly.
Reproduction Steps
Operate a train (difficult to replicate as bug occurs randomly)
Expected Result
Train should exist as normal.
Actual Result
A car in the train disappears, breaking it.
I̶s̶ ̶t̶h̶i̶s̶ ̶n̶e̶w̶ ̶b̶e̶h̶a̶v̶i̶o̶r̶?̶ ̶D̶o̶ ̶y̶o̶u̶ ̶k̶n̶o̶w̶ ̶w̶h̶e̶n̶ ̶i̶t̶ ̶s̶t̶a̶r̶t̶e̶d̶ ̶o̶c̶c̶u̶r̶r̶i̶n̶g̶?̶
Sorry, I see you mentioned May 3. How certain of that date are you?
How reproducible is the problem? Are you able to create a simple repro place?
When the train is missing are all instances for the train not present on the client? Does it disappear when the player starts driving, or some other event?
That is the closest date I have ever been able to provide for bug reports (not sure if that’s a good thing or a bad thing…) which is based on the first time that it has been reported as a bug by our players.
The problem seems to be easily reproducible by the players of our games. You should check out the games that I linked to see if anyone experiencing the problem mentions it in chat (they sometimes do) and if you can reproduce the issue as well. I can assist with this matter if needed.
If this proves to not work, I will provide a place file then.
I am fairly certain that this is a server-sided issue, not a client-sided issue (which may mean that it does not have to do in streaming as my original guess with).
Each car in the train are grouped into three models named Body, Doors, and PoweredBase. Everything in the Body model is welded via a script and attached to Doors and PoweredBase via different constraints. It is this Body model that is affected by this bug and disappears.
I do not recall declaring “JointsService” in any of our scripts.
There is nothing special about our trains that is causing this issue as other games involving trains are also affected by this. Therefore, it is a bug that is server-sided and affects multiple games.
I’m looking into if there were any relevant changes around that time, but not having an exact time and date when this problem started occurring makes it difficult given the volume of changes that are made.
Having a simple repro place with a single train driving in a big loop, or something similar, would help us narrow down what exactly is going wrong, assuming the problem occurs in a more simplified place.
When are you saying you think this is a server side issue are you saying the body model is missing on the server as well?
Are all of your places streaming enabled? It looks like Transit City 3 is not. If they are experiencing the same problem this seems unlikely to be streaming related.
I am fairly certain that this bug affects HingeConstraints as that is what is used in all these games. This should surely help to pinpoint and fix the bug. Hoping that this can be fixed soon as many players in all of these games are very displeased with this bug.
Thanks for keeping us updated on this bug. I work on the physics team and I’m currently investigating this issue.
I released a feature late last year that may be related to the disappearing train cars. I released a fix for these issues on June 5th, so I’d like to triage to see if this fix remedies the issues you’re seeing.
Here’s my plan: I will disable the feature that may be causing the issue on PTA Classic: Kennedy Lines, PTA Subway: FIfth Av Lines and PTA Subway: Callaghan & Madison. If you or your players see any trains disappearing in any of your experiences, please reply in this thread or send me a DM. This will help narrow down the potential sources of this bug.
You say the fix was rolled out on June 5th? The bug is still occurring and has been occurring much past that. It also happened today 2 hours after your post, shown here:
