Samsung seems to have dropped support for external cards in their current firmware, as we know that 3321s used to work as well as many other Samsung smart deadbolts, and recently there seem to be issues popping up. From some basic experimentation done with cards, we determined that they are not accepting anything other than Mifare Classic cards, and it has nothing to do with failed coupling.
The possibility of dumping the firmware from a working lock using JTAG and then figuring out how to flash that onto new locks to give them the functionality back is being discussed here, and @amal is offering a loaner lock to anyone with the capability and knowledge to do so, however as of right now it seems the best bet is to stay away from them.