I am using InDesign CS6 on Mac OS 10.11 El Capitan. For two days I was finding I had severely limited “Undo” history, and found this thread. I deleted the “InDesign SavedData” file in my user/LIbrary/Caches/Adobe InDesign/../../ location, and restarted. I was delighted to find an apparently restored capacity of Undos (tested about 2 dozen steps; before I’d been allowed only 4 or 5, or sometimes even fewer).

Thanks for the help, users!