You'll almost certainly have to show us what you are doing in the extraction before we can offer any kind of explaination or workaround. Like pictures, the code paints a thousand words.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.