Immobilizer problem, car wont start

I have a 2005 murano with 120k on the dash of recent the car doesn't want to start it just cranks.but also it has a check engine light with the code for fuel level sensor. Whenever I have the fuel tank fill all the way up the car start and works perfectly fine but as soon as I reach about half tank it starts to do the same thing ( not wanting to start)
During these periods I won't check and clear the codes using my cheap scantool( it usually has a u1000 and a po463) I always carry in the car and it then starts up but then GREEN key icon keeps flashing in the instrument cluster.
Idk if anyone has has ever experienced this