* Lazy production line worker hand-tightens bolts and forgets to torque them, faking the results on the electronic torque wrench (which records the tightening of every bolt).
* A design flaw causes vibrations which cause these bolts to loosen.
Because of your inclusion of the assumed 'lazyness' of the first I assume that you think it's the first?
why do you think it's more likely that the line worker is lazy and the one that screwed up? why not the 'lazy' designer who thought it would be strong enough, or 'lazy' supervisors that forget to supervise, or the lazy quality-assurer that forgets to assure quality?
Everyone makes mistakes. If your whole organisation relies on nobody ever making a mistake, then your organisation isn't at risk of failing, but is certain to fail. Or alternatively the organisation has already failed in its duties, but the consequences of that failure just haven't popped up yet.
* Improper bolt tensioning process where bolt tension is later unintentionally reduced due to tensioning order.
* Design or material failure where bolt tension post-installation drops more than design allows.
* Miscalibrated or otherwise defective equipment.
* Other failure in manufacturing not caused by the worker, e.g. missed a necessary second or third tensioning pass (different torque or rotation angle) without appropriate failsafes or final validation to discover it.
Bolt tension validation is normally done with an ultra-sonic scan. Torque only provides a rough approximation of the tension at time of installation, and is only suitable where precision is not a requirement.
I suggest https://www.youtube.com/watch?v=XLzTB4KLCxU for those curious about bolts - a very specific, but interesting video.