Undo is not working 2.8! I was just 3d modeling as usual and I enabled the Archipack blender addon. Everything was fine until I tried to undo something and it didn't work. I went to a new project and the same thing happened. I moved a mesh in object mode and it wouldn't undo. My shortcut is CTRL-Z as usual.
I first disabled the addon, which did nothing. I then tried manually going to commands and undoing, and that didn't work. I then checked my keyboard in another program (It works fine). I tried all the blender stack exchange forms, and none of them worked. I updated windows, Gforce, and my driver (Still no difference).
Then as a last resort completely uninstalled blender and its cache, and installed the newest version, and still it doesn't work. I've studied my undo settings and everything, blender is refusing to undo!
You have to enable: Global Undo
For 2.8x and 2.9.
Edit &gt; User preferences &gt; System &gt; Memory &amp; Limits: Global Undo

For 2.79
Just go to Edit &gt; Preferences &gt; System &amp; Setting, and check the Global Undo in Memory and Limits