VM 2.9.6 Error showing product prices for different shopper groups

[nzed]

In my shop all products have two or three prices for different shopper goups, one for Default, and the others for other group(s) that have a reduced price. For some reason only one product shows the reduced price in the shop when the logged is user is in a certain shopper group. How do you think I can find the reason for this?
I can see the same settings at all products, only amounts are different. The testing situation is the following: I open the category page without logging in, so the default prices are shown. After that I log in with a user that is put into a shopper group with reduced prices. Only one price is changed, all others are still show the default amounts.

[Milbo]

I just tested it with different shoppergroups and it works for me. Be aware that if there is more than 1 price possible, it takes the more expensive one.

[nzed]

Maybe I'm doing something wrong. Why does the first (good.png) work fine, and the second (bad.png) show the higher price always?
All other options are the same. I also compared DB records in tables yd2ql_virtuemart_product_prices and yd2ql_virtuemart_products for these products. What else should I check?

[attachment cleanup by admin]

[Milbo]

Maybe one is a derivated product? a child?

[nzed]

None is derivated, no children.
On page /administrator/index.php?option=com_virtuemart&view=product the "Product is Children of" column is empty for every product.

[Milbo]

Thx, I think I found it. I sent you via pm my skype, would be nice you test it first.