Price get set to 0

I have tried this plugin as it on paper sound like it would suit what I need to do, but once active it doesn’t.
I have a variable product (Christmas cards) with 10 different motives, I set to discount to give a fixed amount if you purchase more then 10 (must be able to mix the motives). And then again if you buy 20 and so on.

First time I activated the plug in it worked as long as I had only one variation in the check out basket. And no more than 10. If I had more then 10 it gave to flat discount but then also cut the cost with 50% for all others.
This time it sets the price to 0 if I enter 10 or more.

Either case no good. I’m new to this world so I might have missed something.
Can someone please help?

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