Cart stopped working after update: 1525 Incorrect DATETIME value: ''

-- url of the page with the problem -- : www.screenix.eu
-- HikaShop version -- : 4.4.3
-- Joomla version -- : 3.9.28
-- PHP version -- : 7.4.3
-- Error-message(debug-mod must be tuned on) -- : 1525 Incorrect DATETIME value: ''

Hello,
Our shopping cart has stopped working since the latest update. The following error message appears as soon as you click on the shopping cart: 1525 Incorrect DATETIME value: ''
In the backend it's the same if i go to cart.
All other areas like orders, customers, products evereything seems to be ok.

Does anyone have any idea how to solve this?

Thanks, Romana