Speedybee F405Wing Doesn't stay bound

Good evening Everybody

I’m new to flightcontrollers and im having some troubles!
my main problem is that everytime i take power off the FC, i have to Rebind my Transmitter!

I am using an old dx6i with an Orange reciever, everything works so far until i power the FC off…
anyone got an idea?

Jumping Ground to the Signal wire triggers the Binding in the Reciever…i guess thats somehow an internal problem on the FC?!

greetings from Germany