Good news, everyone!
@spacemig let us know in the SatNOGS chat room that the NEUTRON-1 team managed to decode (partially) and identified the AX.25 header call sign and a few more bytes of signals from SatNOGS observations. So, NEUTRON-1 is still alive and scenarios about antenna deployment failure or about dead battery are not valid any more.
As @spacemig described:
This confirms that we are entering a strange mode where we only beacon a couple times a day like we suspected. We just need to continue to patiently collect more observations and find the right opportunity to send some commands to change its behaviour.
We are going to schedule several observations in Network the next days to help the team and make sure that will identify the satellite before the objects separate too much.