It’s hard to say “what went wrong” in this situation as the life of every wine is a fog of carefully guarded secrets that even my scrying glass can’t penetrate. However, the one thing that sticks out for me in your telling above is the drastic change in environment from your garage to the wine locker. In my experience, it’s better to keep wine, in barrel or bottle, in a constant set of conditions, even if the temperature and humidity is a bit above or below the “perfect” digits.
In contrast, your bottles could just be going through what we call a “dumb phase,” which often happens during the aging process. Every wine has a life cycle and, like humans, often aren’t at their peak when exposed to stresses like moving or a drastic change in the weather. I suggest waiting a couple of months to see if your wine experiences a change in attitude.
With respect to your plans to build yourself a wine storage cellar, I say bravo! Go ahead with your plans with 55 ºF (13 °C) and 70% humidity as the goals and don’t worry about those numbers being the cause of your problems. You’re setting yourself up for some good wine storage conditions, which your wines will appreciate all the more when there from the outset.