> The scientific opinion is that is insufficient evidence to either exclude or include it as a cancer cause but most studies show some increase.

No, this is patently false. Out of all expert consortia, only IARC (= WHO) has reached this conclusion, and it was universally criticised for both the way they report risks (which is highly misleading), and the fact that their publication in turn suppressed contradictory results. All other relevant expert consortia state that the evidence does not support the conclusion of glyphosate and/or Roundup being carcinogenic when used correctly, despite the existence of decades worth of data which should show carcinogenicity, if it had an appreciable effect. “Most studies”, especially high-quality ones, show absolutely no effect.

Is there evidence that it is carcinogenic when used incorrectly?

If there were, I could see a scenario where incorrect usage was so likely or unavoidable that it becomes negligence on Bayer's part.

I don't know if that's the case here; however.

If you drank it I imagine all bets are off but I can't imagine there are many of those studies nor is it relevant to the case.

The question here is whether Bayer /Monsanto knowingly used a carcinogen that nearly every health org says is not a carcinogen.

No direct evidence as far as I know (definitely none for glyphosate, possibly for Roundup) but that’s why Monsanto/Bayer publishes precise usage instructions, and such risk would be based on dosage and wearing of appropriate PPE (= e.g. gloves). In other words: Any risk would be hardly unavoidable.