Optical sorter rejecting a walnut shell, what to do

in the small fruit process (blue berries, cranberries, etc) sometimes the optical sorter, intended to remove foreign material, a piece of walnut shell is found. what would it be the best course of action? any help is greately appreciated.

This is how I'd approach it.

Stop the line, what has been made which could be contaminated with allergens. Put it on hold. Risk assess which will include trace, what load it was in, how it might have got there. Potentially may need to scrap.

Continued investigations might need to establish how did it get there? Beyond, say "it was in X load". What controls are in place? For example, do you insist growers are not near nut trees (not even a neighbouring field) do you insist on restricting what transport can be used? E.g. lorries cannot also be used for nuts. What controls are in place for food brought onto site by harvesters. Basically do an RCA using a recognised method and put in some CAPA. Then make those changes and make sure that CAPA is robust and effective.