I see both sides of the situation and understand each point of view. It is very frustrating when things don't work. Even more so when you are dealing with an elderly person too.
However I think the point some are making is this, if for some reason at your own personal home with your Mom in your company you had a lock to fail, would you never go back. I don't think so. That is the point some are making, crap just sometimes happens. And it does happen at WDW. It is not some magical place protected by some unseen aura that prevents crap from happening, it happens every day; probably every hour, maybe even every minute. You can not have that many people in one place and it not happen. To expect otherwise is unrealistic. Any resort could have this happen.
(This is not commented to the OP), but to posts in general, I think the expectations about what will and will NOT happen at WDW are unrealistic for most.
If SSR does not meet your personal preferences then you are completely right to wish to stay elsewhere. However things will happen at any resort and do.
As to locks. There is no way to know for sure what happened. They might have rekeyed after a maid saw you leave the room. Even though you had not checked out. Did you leave a Do Not Disturb sign on the door. Everytime we leave the room, since we do not get maid service at
DVC we put the sign on the door. It does help. The keys are a pain at times, anything can demagnetize them. Just having them in your pocket or purse can do it. But this happens as much at other resorts as SSR.
As stated it's nice that DVC offers so many choices and everyone can choose what they want. I find the BW restaurants to be as inconvenient as some would find DD to be for SSR. Actually I would guess if you are in the very farthest room at BW in those long hallways and the closest room to DD at SSR the distance difference is minimal if any. We love Artitst's Palette and it would be one of the main reasons to stay at SSR for us.
Hope your next stay home is more to your liking.