Product number won't change

Alright, so I’m working on the website for our bike company and we ran into some troubles. This is pretty urgent and I’ve searched everywhere for an answer. I’m sure it is an easy fix. I hope someone will take the time to help us out, as this is a huge setback to us.

So the problem:

We have several thousand products and they have several things in common. So every time I make a new product I just duplicate the old one and change the necessary stuff. It has always worked perfectly. However, a few days ago, this stopped working. Whenever I duplicate a product and change the product number it just goes to the same it was before. So basically all new products have the same product number even if I change it. It just goes back.

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