Even though most Tetra are omnivores, different fish prefer different type of meal, just like us. One may prefer meaty flakes, others prefer veggie flakes.
Never experienced BNT not eating, unless youfeed them right after turning the lights on. If bellies are full, just monitor. If bellies are tucked in, try different brands.
Frzn foods ( Blood worms, mosquito larvae ) are safer than live food ( can bring pathogens to tank ) unless you knoe how to eradicate them before use.
As long as water conditions and are not infected ( usually their behavior changes when sick ) by external parasites, I would just monitor them.
I used to run Camcorder on the tank when i am not home in order to understand the tank better. Fish will behave differently when you are standing in front of the tank ( Pavlov? conditioning, Psy 101).