RFID module always finds the same non-existent tag when seeking
I have spent the start of time looking into this, but I need to spend more. This is what I have found so far.

The fact that your tag type is 55 is a big deal. The acceptable tag types are:


  0x01 – Mifare Ultralight 
  
  0x02 – Mifare Standard 1K 
  
  0x03 – Mifare Classic 4K
  
  0xFF – Unknown Tag type


Now, to continue from here. There are some error codes that you could get querying a tag type.


  0x4E ‘N’ - No Tag present.
  
  0x55 ‘U’ – Access failed due to RF Field is OFF


There are other commands that also get responses of this type, so I need to research the software to find more, but as of right now it seems that it is sending you back an error code as the tag type cannot ever be 0x55, however almost every command has an error option that can return 0x55.

I hope this gives you some direction, either I will find something or you will find more as you debug to make it possible.

I could be helped if you had a debugger and could show me everything being sent over serial to the device, this would allow me to determine the exact state the error is being generated from.