Hello,

Please add this code to the Theme Settings > Custom CSS > Global:

.cart-widget-side.wd-side-hidden,
.login-form-side.wd-side-hidden {
	z-index: 9999999999;
}

As for the errors, please make the full backup of your site and check the issue on the Storefront theme to detect if our theme causes the problem. Storefront is a free theme developed by WooСommerce.

Best Regards