i dont know whats it called in english but in my way to translate it it would be "circulating torque"
its a force that applies when an axle is supported by bearings and theyre threaded into something,when you pedal the force goes opposite to the rotation,unscrewing your bb.its like the balls of the bearing were planets in a gear hub,they turn the direction around
hence the paradoxon of having backwards facing threads with bsa bb.
loctite it in with medium loctite
edit:
sorry that its german