Risk Management Requirements

It is not clear whether you are referring to your own internal audits or accreditation body assessments.

Any missing or noncompliant process or activity is a non-conformance (NC). Common examples are incomplete method validations or lack of recorded personnel competency.
ISO 17025 does not require a classification as major or minor. The impact must be assessed by the responsible persons on a risk basis.
Typically however, a Major NC would be a missing or deviant critical requirement, i.e. systemic problem  (e.g. no Management review performed, ineffective or incomplete audit programme, or absence of critical environmental monitoring) whereas a Minor NC would be a missing activity, such as mandatory environmental monitoring record not completed for a day. If not evaluated and addressed minor NC could become a major risk.

For more information on ISO 17025 requirements, have a look at 

• The landing page ISO 17025 – Where to Start? https://advisera.com/iso-17025/,
• The article ISO 17025 technical internal audit: The basics at https://advisera.com/17025academy/blog/2020/11/10/iso-17025-technical-internal-audit-the-basics/.
• A previously answered question https://community.advisera.com/topic/non-conforming-work/  
• The article https://advisera.com/17025academy/blog/2020/11/04/corrective-actions-principles-and-root-cause-analysis-in-iso-17025
• Other Advisera Academies' resources for background, for example, Major vs. minor nonconformities in the certification audit - https://advisera.com/27001academy/blog/2014/06/02/major-vs-minor-nonconformities-in-the-certification-audit/