Basic and premium version and vpn

We used the basic version, then purchased the premium version to add a third currency. Default EUR, then USD, then CHF. With set prices, no conversion.

Using the basic version, the VPN works fine. However, since the premium version is installed additionally and active, it does not change the currency based on the VPN any more.
I can enter the settings into the premium version, for example, the CHF pricing, and then deactivate the premium version, and the VPN works again and still knows the CHF pricing, although it is not a setting within the basic version?!

This is so confusing! There is no Cache Plugin at use. How is this possible?

And, since the premium is installed, weird things started to happen. All of a sudden, the freight in USD, is with an additional 2.50 USD.
All of a sudden, a German customer is charged USD instead of EUR. And the freight is a “random” number which does not match any freight amounts entered.

And it is happening randomly. Some customers can pay everything correctly in EUR, correct freight.

How can it suddenly happen, that another person in Germany gets USD prices and random freight?

What is going on? How can the basic version “know” information out of the premium version, if the premium version is disabled? Why is there no way of having the premium version active, neither by itself, not together with the basic version?

And again, there is no Cache-Plugin.

Many thanks for looking into this.