OpenCart 2.3.0.2 - PayPal Payments Standard

Hi I'm using OpenCart 2.3.0.2 and PayPal Payments Standard. Recently, after making a payment, PayPal stopped returning to the index.php?route=checkout/success page, and the message “Your payment was completed. To continue shopping, please return to the merchant.” and the “Return to Merchant” button appear, which leads to the index.php?route=checkout/checkout page and shopping cart is not clearing on the cart page. At the same time, the status of the order changes, IPN RESPONSE: VERIFIED. This happens both on sandbox and live. I tried it on the store site and on the test site, but it does not work correctly everywhere. Please tell me, what could be the problem?

There is a session issue with modern broswers, but that would not affect the 'return' URL. https://github.com/opencart/opencart/pull/8072

Use your web browser's developer tool and check the PayPal form fields at the last step of checkout to see if the 'return' URL being sent to PayPal is correct.