To anyone who has experienced this -- just out of curiosity, were you on a different device when the game level reset to 57? Or were you using the same device?
This has happened to me twice now... First I was Level 57 and got reset to 56. Then I was at 58 and got bumped down to 57. Both times I installed the update on my iPad first and bought the new buildings. The next day I opened the app on my iPhone at work and the app did an automatic update. When the game loaded, my level had been reset, the cash I had used to buy the buildings was gone, but I no longer had the buildings in my town.
It would just be nice to know if this is a glitch, or if something I'm doing (e.g. switching devices) is causing this issue.