NFC tag can be active if no relative movement of tag-reader is there?

Question

We are building a NFC application which requires the NFC tag to be read once (by a Android mobile device), the data is then Sent to a server which processes it and the processed results are sent back to the device which writes the data back to the NFC tag.

Operations performed by the mobile device (which has a NFC reader) :

• read data from tag
• send data to server and wait for processes results
• receive the processed results
• write results on the tag

The problem is that when the time taken is higher than half a minute (due to network speed and processing time taken on server side) the fourth operation (writing the processed results back to the tag) fails.

A few possible reasons for the failure could be :

• A : the tag is powered by movement of the tag within the magnetic field created by the reader. By the time the second and third operations are finished and the fourth operation is tried, the tag doesn't have power anymore.
• B : our code has a bug and the reader / tag-object should be freshly created for the fourth operation to be performed (we keep the reader and tag objects in memory while the other operations are performed)

The code/library (to interact with the tag) used in our Android app is provided by a third party. My knowledge of NFC ( and the ndef Android library) is limited. what I am looking for as a help from the community (if someone has experience in above situations ) is the following

• if above is happening because of B. We would try to figure the same out. (Or approach the third party vendor to give a solution)
• instead if the reason for the failure of the fourth step is due to A, our debugging of the third party code is useless. (Effectively what we need is that we change the process so that the application prompts the user to tap the tag once more before the fourth step happens)

Answer 1

I would separate the 4 steps into 3 groups.

1) read the tag
2) send data to server and wait for processes results, and receive the processed results
3) write results on the tag

1) is a user interaction ("please tap the tag"),
2) happens in the background ("processing data") and
3) is again a user interaction, where I would aks the user to touch the tag again once the data is back from the server ("please tap the tag again").

This helps to separate the steps, which have undefined timing (what if the phone has temporarily no data connection? It is also difficult to expect that a user wild hold the device steadily over the tag until the data is back.