Ciao Matteo,
I worked in the past with NFC Tag and I had the same problem, this happens (my opinion) because there isn't in the manifest the android.nfc.action.TECH_DISCOVERED, the nfc_tech_list.xml in the apk and there isn't the foreground dispatch (I tried to solve in my extension but I could not) that tell that your app has priority other app installed that handle the same intent.
I wrote this that could help You to understand.
If You want You can try my extension that use Mifare Classic and Ultralight it depends what You want to do