Actually this is not accurate… it is not the cloner that is the issue… the T5577 chip itself is to blame.
First read this;
https://forum.dangerousthings.com/t/quirks-of-the-t5577-cloning-tags-to-the-xem
Then read this;
https://forum.dangerousthings.com/t/xem-cloning-emulation-modes-and-the-perils-of-chinese-cloners
In short @StoicMaverick it may be possible to recover your tag. I will be working with @TomHarkness to eventually create a clear “how to” guide for doing just that, and we are also working on a new proxmark3 antenna that will couple well with the xEM.