RF37S114: Writing to tag works, but sometimes tag response contains error flag set with error code 13

Tool/software:

Setup: NFC Reader CLRC663 from NXP (without library)

Request Flags: Option Flag set, high data rate requested 

Command: Write Single Block 0x21 command 

The RF37S114 response after write command returns in about 50 % of the cases error code 13. The tag is locked within its case so a movement outside of antenna area is impossible, inventory and read commands works smoothly without any errors. 

I wait for 12 ms, after sending EOF symbol to ensure time delay is at least 10 ms and tag is able to respond correctly. 

What could be the reason for the error?

I write a simple 8 bit value to each byte of the block and increment it afterwards. Even when I receive the error 13 the data which are readed out in the next task contains always the updated value. Should I ignore this behavior?

Kind regards 

Sascha Winkler