As far as I can assume this problem occurs because retainers and player characters are not backed up at the same time. It would appear retainers are backed up either before player characters or more frequently. So this creates a situation when a crash is happening there is potential to loss items you remove from a retainer. Typically these roll backs go further back then when the problem is noticeable by the players. Typically when this particular crash happens you won't be able to do anything but chat in game. However, it is rolled back X minutes before that and if you took and items from a retainer in that time frame say goodbye to those items.