Alright, after trying it again, I realized that my old save had actually saved my resources, but not the things I had built. I had built improvements for wood and metal, among others, but they weren't there. Gathering those would give me 10 materials and take 3 seconds, consistent with the room not being built.
After deleting the Hope folder as you told me, I played a few turns and the same thing happened again. I built stairs, then left, and on playing again the stairs were not there (but my resources were).
I will try again in the next update. And, if I'm the only one having the issue, don't worry too much, it may be something on my end.