Error - order has less products then cart - Prestashop 1.6

[sitte]

On Prestashop 1.6.1.22 I have huge problem with some orders from time to time. When clients are finishing their orders all looks fine, total amount is proper but order has much less products then the cart witch was used to finish this order.

Example:
Cart has 20 products, total amount 380pln
Order has 15 products, total amount 380pln

It looks like not all products from cart are transcribed to order.
I upgraded to prestashop 1.6.1.22 (before there was 1.6.1.17), I replaced payment module but no result.

It happens on different products, not every time, there is no chance to triger it

Any ideas?
 

Edited February 4, 2019 by sitte (see edit history)

[musicmaster]

Did you check the error log of your server?

If that doesn't work you should start looking for javascript errors. That means making console visible and then placing orders yourself until you get the bug.