Create Contraption models disjoint at random, SPECIFICALLY in multiplayer
To preface: I've been working on a personal modpack (Minecraft ver. 1.19.2, Fabric loader ver. 0.15.7) for a friend group of mine, and I also host a server which runs that modpack. Notably, it includes Create Fabric (ver. 0.5.1-f-build.1416) and Iris (ver. 1.6.11). I've been gradually debugging the modpack for a long time now, but there's one bug in particular that's been particularly difficult to pin down: The main mass of a Contraption's model (all of the non-animated cubes) will sometimes split off from the contraption's actual location, appearing skewed and displaced in ways which depend on the viewer's position and their aim direction. A demonstration of this can be seen in the attached clip.
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When the bug is active, any angular differences between the world's North and the player's aim direction will essentially be mirrored on the Contraption's main body. Looking up causes the Contraption's model to rotate downwards around the player's position, looking right causes the Contraption to rotate left around the player's position, etc.
A troubling part of this bug is that it's been quite difficult to pin down its causes. The train Contraption shown in the clip is the only case we've found where the bug is active near-constantly; most Contraptions on the server only display this disjointed positioning in short, seemingly-random bursts, if they ever show it at all. Every single attempt we've made to intentionally recreate the bug in a singleplayer world has also failed, making it especially difficult to diagnose its cause.
The only thing we really know for certain, at least so far, is that this bug is linked to Iris in particular. Eliminating clientside mods one at a time and checking via this highly-volatile train Contraption has shown that the visual displacement will only ever occur while Iris is installed. The viewer's shader choice (including no shader at all) has no effect - it's just whether or not Iris itself is there.
Any assistance in diagnosing this issue, or figuring out some sort of workaround, would be much appreciated. Please ping me with any responses.