[FIXED] [GRO] Tank top visual distortion (bad polygon?)

I just came to report the exact same issue!

Doesn't matter what body size/shape your sims has.

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.96.365.1030
What expansions, game packs, and stuff packs do you have installed? All.
Steps: How can we find the bug ourselves? Enter CAS, select the Growing Together camisole and turn the sim around.
What happens when the bug occurs? During animation a part of the shirt on the back right near the underarm stretches noticeably different to the surrounding parts.
What do you expect to see? The shirt should move as a cohesive unit.
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Neutral/Not Sure 

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Using modding tools I've identified that it's a single vertex with the wrong weight modifiers assigned causing it to move contrary to the surrounding parts.

So many of their recent CAS assets have had so many issues. I don't remember seeing this amount of easily fixed CAS bugs back in like 2016

@unicornpiggiezyeah that's the one I was talking about, it's actually three vertexes that are taking up the exact same space. I also don't know much about blender but I was able to assign them the missing vertex groups spine 0, spine 1, spine 2 and right clavicle with the correct weight modifiers for each group. I'm not sure if we're allowed to link to mods here but I put it up on curseforge under my other username gay4space.

Happens in Live Mode too, particularly when interacting with an infant. Other times is less noticeable.