SC2Mapster

Apply a Buff to the harvesting unit that modifies the Resource Harvest Amount Bonus using a Set effect that only applies one of the Apply Behaviour effects. You can have the buff removed by the resource carry buff which also disables the applying behaviour as does the random factor buff.

Give the units that do a mining a Buff behaviour that uses a periodic Set effect that uses Apply Behavior effects which apply a second Buff behaviour. This series of second buffs disables the first one preventing multiple applications and boosts the mining amount. The second buff is removed by a Unit Compare Behaviour Count validator that looks for the buff applied by the resource. A second validator disables the first buff if the unit is holding a resource.

Under the unit you want the Units data type you want the Behavior: Behaviors - Behavior field.

On the first Buff behaviour under the Behaviors data type you want the Behavior: Validators (Disable),  Effect: Effect - Periodic and Stats: Period fields.

On the Set effect under the Effects data type put your Apply Behaviour effects in the Effect: Effects field and set the Effect: Maximum Count and Effect: Minimum Count fields to 1 and Effect: Random field to Enabled.

With the Apply Behavior effect (also under the Effects data type) put the second buff in the Effect: Behavior field and set the Effect: Unit - Value field to Caster.

With the second Buff behaviours under the Behaviors data type you want the Behavior: Validators (Remove),  Behavior: Modification - Behaviors Disabled and Resource: Modification - Resource Harvest Amount Bonus fields.