Default variation does not working

Hello,

First of all, I want to thank you for the great plugin that I really like,
the issue is, I set up a default variation for products, if I go to the shop page the default variation is selected but when I click to go to the single product page for customization, the default variation is selected but it becomes unselected after 1s loading time,
I am using the Fancy Product Designer with the Variations plugin, I tried a plugin to force default variation but it doesn’t solve the problem.
and even if I select a product on the shop page and click customize button, the single product page appears with no selected variation.

Thank you