Bambora Payform - Session expired after some payments instead of checkout_success

[zamzom]

Thank you for this crutial info,
Additionally, at the current state of Chrome browser SameSite=none; also causes error.
You can not even log in to the site, it automatically logs you out.
In the page error report it says Secure connection is obligatory if SameSite=none choosen.
So the below definition by DrByte should be changed as follows:

define('COOKIE_SAMESITE', 'none; secure'); 

Please forget the previous suggestion. init_sessions.php searches for exact phrase 'none', if you change it, it won't work.
Page encoding should be https though, otherwise samesite 'none' will create an error.