I send multiple items on a daily basis, buying the postage online which then sends QR codes in an email so I can go straight to the post office and scan them in. Bang, bang, bang down the list of orders awaiting dispatch, all within the UK, there should be no issues. But sometimes, not all of the codes come through - today I had 10 items and only 5 codes came through at random (not in the order of the items sent). It doesn't help to go back in and re-order the code, it still doesn't appear. The codes will come through eventually, but it can take several hours and sometimes this means the items can't be handed in at the PO until the following day. This means they are sitting in ebay's system, marked as dispatched, when they are not, and there is nothing I can do about it! What's holding up the delivery of these codes? It's an infrequent but recurring glitch, and apart from the annoyance to me in planning my trip to the PO, it holds up delivery to the buyer.
