There is a bug in version 1.3.8 of WaiterOne. As we are preparing a new update to fix this bug there is a workaround for it so you can keep on working without any problems.
The bug is seen on the bill, the number of articles are less then the ones ordered, quite annoying, the total amount is correct though. The workaround is very simple : activate the cumulate PLU’s on the bill printer. Go to data -> printers -> (your bill printer) -> enable the ‘cumulate PLU’s’ switch :