My experience as Plat is that my priority F tags do seem to fall off every once in a while, although luckily that usually only happens after they are loaded into the right container. It has to do with the quality of the tag material, which allows them to easily rip. And at some stations it also has to do with the fact of how they attach the priority tag to the baggage tag (eg., in ZRH): if it is too close and tight to the bag handle itself, it is much more likely to rip off.