The only way to fix cross-contamination issues is to have a different production facility for every possible combination of allergens.
Which is insane.
I worked in a factory that packaged food, if one product contained an allergen, there was no way you could guarantee that a tiny amount of that allergen wouldn't get into some amount of the next product on that production line. No way. Not any possible way. You can clean all you want, you can do whatever you want, you can mandate whatever procedures you want, but there's just no way. Even if every half-awake half-sober completely uncaring third shift production worker (like 1990's era me) does everything exactly right, which they won't, even if they actually cared to, which they won't.
The FDA is putting manufacturers in an impossible position, and it's insane.
I have food allergies, believe me, I get it. But there's just no way. If a manufacturing facility produces products with tree nuts, someone with an allergy to tree nuts has to treat every product produced in or near that facility as though it contains tree nuts. That's reality.
The FDA is not dealing with reality. The problem here is the US federal government.