Help with Prices changing after orders please

[Gingerweb]

I am struggling to get the vat (adding 20% to everything) to work properly, would appreciate a hand if someone could point me in the right direction!

VirtueMart 4.2.4 10922
I have created a single tax rule set at +% for 20 - everything else pretty much is blank so it applies to everything.

I have quite a few products with variants and this is where it seems to be going wrong. Initially when i set it up the product displays properly, but once an item has been placed in the cart the price changes, adding another 20% on.
This is a recording of this happening - add to cart, in cart you can see the extra 20% is added and then when you go back to the product it is 20% more
https://support.gingerweb.co.uk/8LuldpBb

This is the product so you can try it yourself and see the price go up!: https://sphsupplies.temp-gingerweb.com/index.php/shop/dogs-15/protective-wear-26/flecta-hi-vis-dog-jacket-detail This "price rise" is unique to the browser window so if you then open the product in a private window the price will be the lower one again.

attached are screenshots of the Adult price and the Variant prices for the top ramifications.

Extra context: The data in the shop was migrated from Prestashop using Cart2Cart, does anyone have any experience of this kind of migration causing issues like this? This product though, and many others, have been created from scratch so we arent using the same variants for this product. I have setup this template on a clean site and setup a couple of products with vat and they work perfectly, i have compared installations and cant find anything different.

thanks for looking