Say we have something like this:

Scriptname ReducedSpeed extends activemagiceffect  Event OnEffectStart(actor akTarget, actor akCaster)	akTarget.ModActorValue("Speedmult", -20.0)EndEventevent OnEffectFinish(actor akTarget, actor akCaster)	akTarget.ModActorValue("Speedmult", 20.0)EndEvent

It's attached to a spell with constant effect, the spell affecting an armor part. You equip these heavy armor boots, you're supposed to run slower. Is there a reason why it doesn't actually take effect until I reopen and close the inventory? If I just equip the boots and close the inventory nothing happens, although player.getav speedmult reports the correct altered value. What's wrong?

When changing Speedmult, you must also change the actor's carryweight by a small amount afterward to give the engine the kick it needs to update the value. Generally I use:

akTarget.ModActorValue("Speedmult", -20.0)akTarget.ModActorValue("CarryWeight", 0.1)akTarget.ModActorValue("CarryWeight", -0.1)