I have also experienced a similar issue of the corrections bar disappearing. Its not the most convenient fix but I've found that unticking the button (i.e to hide the correction bar even though its not visible anyway) and then rendering out at a different output resolution will allow you to press the button again and see the corrections bar.
As long as you're using history you shouldn't lose anything, as the resolution change refreshes the frame buffer. Again not the most convenient of solutions but quicker than restarting Max.
Hope it helps