Checkout returning customer error Warning: Undefined variable $action

Hi ,
after recent upgrades, we encounter an error on the checkout page, when user is not logged in:

Warning: Undefined variable $action in */wp-content/themes/xstore/woocommerce/global/form-login.php on line 34
style="display:none;">

Cleared cache, no change.

I digged just a little more, and added the following code (temporary) in the form-login.php file and it works for the moment:

$action   = $action   ?? '';
$hidden   = $hidden   ?? false;
$message  = $message  ?? '';
$redirect = $redirect ?? '';

after

if ( get_query_var( 'et_is-loggedin', false) )
	return;

I know this isn’t a long-run solution, but I am asking what could cause this error and what is your solution?

Thanks team!