Bit late to the game, but regarding stainless steel fasteners locking up solid, for no reason, it is a real problem, as they do it at random, and will not come undone, having to be cut out, drilled out, nut splitter might work?
The answer has been found to be Copper Slip grease, a very small amount at the start of the thread, every bolt, even ones with Nyloc nuts, leading to the use of lubricant on a friction fit item!
Been working with S/steel for many years, this is the only way I've seen work.
Bod.