My camp is "weakened first, then cunning". I put out the math situation previously, but I will posit a new argument:
"Conflicts", RRG Page 9:
While attacking, mission rules are resolved first, followed by effects from the attacker (including figures friendly to him), then effects from the defender (including figures friendly to him).
Weakened would never be applied by a friendly figure, and while it may affect the defender, is a harmful effect, and thus would be considered as an attacker effect. Thus, Weakened would resolve first, cancelling Cunning.
I fail to see why Weaken is an attacker effect .
Even without considering that the defending figure do not cause Weaken to itself, Weaken is a condition present on the defender figure (and most probably not even played on the defender figure by this attacker).
So, for me, the rule you mention imply that the defender has two effects ( Cunning and Weaken ) and has to decide the order they are resolved.
And based on this I can see now, as Norgrath mentioned, that Lock on is an attacker effect and thus, by this same rule, would be applied first, negating Cunning .