What it requires. Multiple conditional setdefault rules target the same assignment.
Why it matters. [doc + reasoned] "When multiple setdefault rules target the same assignment in the RHS, evaluations can conflict" and "only the last rule will reliably evaluate" (CML Best Practices) - earlier rules are not merely lower priority, they are unreliable. The configured default depends on evaluation order the modeller does not control, and an edit elsewhere can flip it.
How to fix it. Consolidate the conditional logic into a single derived variable with one setdefault.
Source. Salesforce CML Best Practices (developer guide)
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