I am now using PyCharm 2018.2. Unfortunately, no local history is saved for any of my files. When I right click on any file and select Local History, the 'Show History' is greyed. "Invalidate caches and restart" didn't work on me. I also checked the idea.log file and I found these:
(2018-10-10 20:13:46,623 [ 5348] INFO - .history.utils.LocalHistoryLog - local history version mismatch (was: 0, expected: 6), rebuilding...
2018-10-10 20:13:46,623 [ 5348] INFO - .history.utils.LocalHistoryLog - FS has been rebuild, rebuilding local history...)
So what does the 'local history version mismatch' mean and how can I fix it?