You maybe know the problem; you are updating or creating a set of items using the JSOM and the changes are made to only one item. The reason is that the process in the back (Event Receiver etc.) can handle only one item at the same time and if it takes to long it misses the update event for the other items. So you need to make sure the update waits until the update before is done. The deal is that the JSOM context works asynchronous. Some of you are using promisses or methods like that. I made a solution that is working without any other library.