Well there have been cases of account being sold or false documents being used to verify accounts and if a user is asked to re-verify his/her account is unable to do it or does it but this time with a different document or the details of the old and new documents doesn’t match it would mean that either the account changed hands or a forged document was used initially for verification purpose.

I have seen other reputable gambling sites asked their users to re-verify their account so this shouldn’t be a big deal for you as long as you’re not doing anything wrong.