Plugin is not functioning properly, it random send out gift!!

Hi there,

I setup 3 gift packages:
1. order above 377 get free 1 stick
2. order above 567 get free 1 box
3. order above 945 get free 2 boxes plus 2 extra item

When I tested it, everything appeared correct, but when customers place orders, some orders receive the gift set while others do not. Could this be due to an inconsistency with the plugin? I provide the login details in a private message to check the issue, pls help!