The auditor’s primary course of action is to evaluate the impact of the partial compliance. When a control is only partially operating as designed, the auditor must first assess significance: what risk remains, what objectives are affected, and whether the deviation is material enough to become a reportable finding. ISACA audit and follow-up guidance emphasizes capturing and following up on significant issues and deficiencies, which implies the need for impact evaluation before deciding on reporting or recommendations.

Option B is correct because evaluating impact is what determines the seriousness of the deficiency and the appropriate audit response. Without understanding the effect of the deviation, the auditor cannot appropriately decide whether to escalate it, report it, or recommend redesign.

Option C is important and usually happens during audit communication, but discussion with control owners is not the primary analytical step. The auditor must first understand the risk and significance of the partial compliance.

Option D is incorrect because not every partial deviation should automatically become a final-report finding. The auditor should first evaluate whether the issue is significant and reportable. ISACA follow-up guidance specifically refers to significant issues/findings.

Option A is also incorrect because recommending redesign may be appropriate later, but only after the auditor understands the impact and whether the problem is design-related, operating-related, or user-adoption-related.

Therefore, B is the best answer because impact evaluation comes before escalation, formal reporting, or redesign recommendations.

References (Official ISACA):

ISACA Journal, Enhancing the Audit Follow-up Process Using COBIT 5 — significant issues/findings should be captured and followed up.

ISACA Journal, An Approach Toward Sarbanes-Oxley ITGC Risk Assessment — supports a risk-based evaluation approach focused on control process areas.

ISACA, How Effective Is Your Cybersecurity Audit — effectiveness depends on evaluating gaps and their implications.