Welds not staying attached in-game, but fine in playtest

Recently, I’ve discovered an issue with my game regarding couplers on the trains. They use welds to connect to eachother, and work fine in play-test but not in the actual game.

I have no clue what causes this, or what fixes it, it first appeared out of nowhere when I was only doing map-related updates to the game. Sometimes if I regroup and ungroup them all they start to work but this has only happened once, and often they will fix themselves.

Playtest:
playtest

In-game (Not studio)
ingame

Special notes:
Couplers are connected to the bodies of the traincar, not the moving wheel-group
This only happens in this specific game, the models work perfect in other places.

Any help is appreciated

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I am beginning to think that this may be an issue with loading the game itself?

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Never breaks on the “Play” feature but will break if it is an actual Roblox server running.