Check out page freeze while using Woocommerce Gift Card

Am still a beginner and I’m experiencing recently a problem at the check out page which gets stuck in the final stage.
It took me a while, but I figured out that the WooCommerce Gift Card (version 2.5.8) is probably causing this issues, as orders paid by bank are coming through in the right way.

This is what happens with the Gift Card:
Once the Gift card number has been applied and the customer wants to do the final check out the whole site gets a kind of stuck (all the colours become a bit more vague). We do receive in Woocommerce the new order, but the customer does not receive any confirmation and is left with a frozen screen.

We already sold the Gift Card to several customers so we just cannot simple go for another plugin and am wondering how we can get this working again. Till now it was always functioning well.

Any ideas??

Best regards,

Alexandra