Well, welcome to Boston. Totally love the city and everything, but temperature shifts of +- 20-25F during the same day are absolutely normal. Spent last 4 years there attending Berklee College Of Music... great life and musical experience, not so great for bass necks.
On my USA Fender 5 I had to re-setup the bass almost everyday, I just gave up and stick with a higher action. That's why I now have a 5-piece neck bass with titanium reinforcements.
Btw, the twisted neck problem was in my first Berklee year on a "boutique" jazz bass that I later sold. One piece maple neck, birdseye fingerboard. Got the bass used, but these new go for $3.0-3.5k... just sayin'.
Lived and played in Boston from 1973-78 and still didn't encounter that despite living in a rented half of a 2-fam house in Newton Centre that still had steam radiators and a gas converted coal furnace. No AC in the summer either. All we could afford at the time were fans to keep the electric bill down.
At the time I owned a '74 Gibson Ripper, a Fender JB, and I was babysitting a Ric 4001 for a friend. None of them warped. Nor did anything owned by the two guitarists and the drummer I shared the space with. Between us we had maybe 15 instruments (if you count the drumkit as one instrument). No environmental issues with anything other than keeping the drums in tune.
But whatever. If it happened to you, it happened to you and I won't dispute it.
FWIW I live down by the LI Sound in CT about 50 miles due east from NYC. Winters aren't as bad as Boston's here. But they're wetter, and the summer is more humid with all that water 4 miles from my place. Still haven't run into necks twisting or warping on anything since I've been here. So either I'm unusually lucky or just the opposite is the case with you. Bummer if it's so.
