Exchange Rate wrong on specific countries / Specific Cases

Hello,

We have a problem with the currency calculation on our site:

We were able to reproduce and analyze the problem that occurred on several of our orders:

1/ A customer arrives on the website, and he is physically in the UK on IPhone / safari.
2 / at the beginning of his session, the website displays GBP, the prices are all UK
3/ He goes to payment and logs in
4 / Once logged in, the whole website has switched to EUR, and the price is 112.49 tax excluded, which is the right price. On the other hand, he has a shipping flat rate of 50 EUR (which is wrong, but as he had not entered any country on his account yet, the system shows him a flat rate in the meantime).
5 / It launches the Paypal payment, but it goes backwards
6 / he enters his address information in the Checkout and therefore enters United Kingdom at this stage in the checkout.
7 / But here, the wrong price of 124.19 EUR with taxes appears (=103.49 EUR tax excluded) with a shipping price also wrong (14.35 EUR with taxes when it should be 15.60 EUR with taxes)
8/ He pays
It seems that when the situation starts to bug, the system considers that the “official” amounts of the site are CHF (which is the place our shop is), which it then transforms into EUR.

Here is a specific example to illustrate this hypothesis:
Official price = 112.49 EUR tax excluded => 134.99 EUR with taxes
Wrong price = 103.49 EUR tax excluded => 124.18 EUR with taxes

We believe that the system arrives at a final price of 103.49 EUR as follows :
1/ It then considers that the official price is 112.49 CHF tax excluded.
2/ It applies an exchange rate to arrive in EUR: 112.49 / 1.0869… (exchange rate EUR/CHF) = 103.49
3/ Then he displays this price (103.49 EUR HT and 124.18 EUR with taxes) as the new price, and this price goes until the final payment.

Shipping price for 1 piece of 1.8 kg:
Official price = 13 EUR tax excluded=> 15.60 EUR with taxes
Bugged price = 11.96 EUR tax excluded => 14.35 EUR with taxes

We think that the system reaches 11.96 in the following way:
1/ It considers then that the official price is 13 CHF tax excluded
2/ It applies an exchange rate to arrive in EUR: 13 / 1.0869… (exchange rate EUR/CHF) = 11.96
3/ Then he displays this price (11.96 EUR tax excluded and 14.35 EUR tax included) as the new price, and this price goes until the final payment.

So we do have a calculation problem related to currencies.
And this problem seems to be created when we inform a country of delivery when we log in (and possibly as a guest).

On the other hand, we have the “Product Feed Elite” module installed for our “Google Shopping” campaign management and the problem seems to have appeared since the installation of this extension, is it possible that this has something to do with it?

Thank you and have a nice day