Ion Petroianu, VA3NOI
Your uBitx V5 uses a different IF frequency (11.059MHz), so your BFO frequency should be lower than that. 11,996MHz BFO frequency was used in V3 and V4. Those two previous versions used a 12MHz IF.
The fact that you receive a horrible signal in a nearby receiver can be related to overloading the receiver. I hope you are using a dummy load on uBitx and the receiver, if located in the same room, should not have any antenna attached to the input.
I would concentrate on the receive function first. Once you are happy with the result try transmitting and monitor your signal using a web SDR.