It most likely is a code related issue. Did you change things in code in the last 2 days? In the past we have seen issues with that code interfacing with many phones and tablets.
We are releasing a production ready NFC stack, (next week I believe), that has much better P2P performance. Unfortunantly the stack won't fit in the current EVM but it will run on a MSP430F5429 / TRF7970ATB combo.
Thanks,
JD