My coworker and I ran the new 18.0.1 update on our computers yesterday. Both updates appeared to have been successful and we proceeded to process images over the next hour. We both at the same time started getting scratch disc errors. We proceeded to delete out all our temp files. This did not fix the problem.
We decided to take a closer look at our C: Drive. It appeared full. This was weird as we both had around 300GB available earlier that day. We ran a defrag just to be sure it wasn't a windows problem (We are running Windows 7.) This cleared up the 300GB.
However once we started retouching images again the Drive would rapidly lose space again. in one photo save my coworker lost 20GB. My coworker lost 300GB in an hour and I lost 250 GB in the same hour.
We have reverted our versions of photoshop back to the previous version and this seems to have fixed the problem. However we would really appreciate if someone could look into and fix this issue in the next update.