If the last stack of blessed combat for either a ranged weapon or melee weapon is consumed it will not apply the damage buff.
You can easily test this by getting 6 stacks and consuming them all on a training dummy. You will notice the damage buff not applying to the sixth attack.
The last stack is significant as you often try to gain 1 ranged stack by swapping quickly to melee combat to enhance the damage of your next ranged hit. If this 1 stack is consumed it will not apply the damage buff.