I have the same problem after updating to 4.1.7, when i create a post and publish it there is no problem, but when i try to edit a post after updating all the custom fields get emptied.
There is a serious bug with the new version and for now i’m going to use the previous version. I couldn’t find the 4.1.6 but I’ve downloaded the 4.1.5 version here:
https://github.com/elliotcondon/acf/releases
