I'm assuming your question is "What if the client already closed the minor NC for last year, however this year we still find the same issue. Is it minor or major?"
Considering that, if you found the same issue that should be solved by a previously issued NC, this means that the NC treatment was ineffective, and this would raise a major non-conformity because it means a mandatory requirement of the standard was not fulfilled.
Please note that minor and major non-conformities are generally used for certification audits, not internal audits, and major non-compliances identified during ISO 27001 certification/surveillance audit, can lead to problems with the certification process.
These articles will provide you a further explanation about the impacts of non-compliance: