Broken FlexM1 Magic

My guess would be that it’s just a coupling issue, and not a failing implant.

This mod for that cloner may interest you and help you get better performance:

The LF side of the NExT is vulnerable to bricking due to poor connection during writing, so everything you can do to get a better connection helps.

If you have a relatively recent iphone, you should be able to read nfc tags with it, I believe the antenna is usually in the top edge, but you can look for your specific model in the NFC Phone Performance Wiki for more specific advise