The code completion features in CLion are not working when a #include uses a backslash. The code compiles fine but CLion reports that the file is not found by the IDE. This causes the UI to report lots of false errors because it cannot find the datatypes and definitions for things that are in this header file. It wouldn't be a problem for me to change the code that I own and manage to use a forwardslash but my project includes headers from libraries that I don't manage or own so this is a show stopper for me. Honestly I was extremely surprised to even find this problem today because I have been using CLion for well over a year on Linux & Mac based projects without such an issue.
I found the following bug report that was filed by another user that covers this topic: https://youtrack.jetbrains.com/issue/CPP-5753