The dynamic resolution setting is still broken for me. It has been broken since March irrespective of cache optimizations or updates. It's now painfully standing out like a sore thumb after my FPS dropped from 60 to the mid 20's until I manually adjusted my resolution.
After playing a bit with the settings I can confirm the problem is limited to fullscreen mode. If I set the game to borderless window I can definitely see the automatic dynamic resolution setting kicking in; it's quite visually noticeable and my frames remain locked at 60 (Also using in-game FPS counter and Rivaturner).
I tried several combinations with or without VSYNC, anisotropic filtering, and anti-aliasing methods. The only setting that disables automatic dynamic resolution is fullscreen. I don't know if this is the expected behavior.