Consultant becoming internal auditor

Answer:
I can give you my own experience; I have done that several times without problems raised by certification bodies.
If you check the definition of auditor on ISO 19011:2018 versus the one on ISO 19011:2011 you can see that the independence requirement was dropped. See also ISO 9001:2015 clause 9.2.2 c), what is important is to ensure objectivity and impartiality. I work on that by preparing my checklists and leaving audit reports that describe precisely what I found.

You can find more information about audits:
- Article - How to write a good ISO 9001 audit nonconformity? - https://advisera.com/9001academy/blog/2018/04/24/how-to-write-a-good-iso-9001-audit-nonconformity/
- [free course] ISO 9001:2015 Internal Auditor Course - https://advisera.com/training/iso-14001-internal-auditor-course/ ernal-auditor-course/
- book - ISO Internal Audit: A Plain English Guide - https://advisera.com/books/iso-internal-audit-plain-english-guide/