I can speak only of my suspicion that it's an unwitting error. I think the extent to which it's witting is that, when these companies and many others decide to go into China, they opt to play by the rules that exist there. Everyone knows what those rules are, and one of them is that there are fundamental prohibitions against core things that you would need to check your supply chain for.
For example, on the ability to do spot checks on processing plants, you don't show up unannounced to a Chinese processing plant. You need permission, and those folks must know in advance. If you can't do spot checks on a processing plant, you can't get an honest assessment of whether there is forced labour in that processing plant. When companies go into China, they know the rules of engagement, and they make a decision. That's witting; that's not unwitting.
Whether this company or many others knew that they have North Korean or Xinjiang forced labour in the plants, I somewhat doubt, but they didn't know for reasons that they did know, if you understand what I'm saying.
A similar point I would make is that when it comes to on-water crimes, the IUU crimes of the vessels at sea, there is also an industry-wide witting blind eye turned to the fact that spot checks are not done on vessels on the high seas, Chinese or otherwise. When you're getting your catch from vessels, even if you have a certain amount of supply chain traceability and you know roughly what vessels that specific catch is coming from, you don't know what's going on on the vessels. Also, you probably don't know what's going on in terms of where those vessels are fishing and what gear they are using.