There is an error in the Venom Master skill in the Playtest 3.1 document. Some sentences that conflict with the new rules for using and stopping Alchemy were left in by mistake. This will be fixed in the Palytest 3.2 release, but for now please consider the following sentences:

Therefore, a blow that strikes a weapon or shield does not use the venom on the weapon.  A blow that lands, but is blocked by a martial or magical skill, does expend that use of the venom.

To be replaced with:

Venom applied to a melee weapon, is stopped by the Dodge, Sidestep, and any other physical defense that stops damage, but the poison or venom is not expended. If such a defense is used the character may swing the venom again for their next attack. Venom delivered by bow or thrown weapons is expended if they miss their target or if the target calls any appropriate defense. In all cases, the Venom is expended if the character lands a successful blow or a magical defense that stops physical attacks is used.