I'm seeing this in logs although it doesn't seem to break anything.

Calling hook CanMoveItem resulted in a conflict between the following plugins: FurnaceSplitter - True (Boolean), ChestStacks (False (Boolean))

Well, it just means you configured ChestStacks that way so it trying to stop player from moving item (for example you limited stack size to 0.25 or something) and FurnaceSplitter is trying to allow that move. You should either chose what plugin to use, or configurate them with this situations in mind.

Here is a video of my players multiplying their ore with the current ChestStacks version - this was never a thing before the recent updates. I've included my config as well so you can test it. Whether or not you think it's a problem with ChestStacks is your decision, I'm just providing the info. Bear in mind that many servers use both ChestStacks and FurnaceSplitter so this does cause an issue one way or another, and FurnaceSplitter doesn't have any config options at all.

https://streamable.com/rhfm8i

{
  "Global settings": {
    "Default Multiplier for new containers": 5.0
  },
  "Stack settings": {
    "Containers list (PrefabName: multiplier)": {
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      "assets/bundled/prefabs/static/small_refinery_static.prefab": 5.0,
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    }
  }
}​