I'm frequently using different computers for Arduino development, so I keep a sketchbook on my OneDrive, and it worked without problem till latest Windows 10 Fall Update. After the this Windows version update (I'm currently on build 16299.rs3_release.170928-1534), even when I set the whole sketchbook folder as "Always available offline", Arduino 1.8.5 can't compile any sketch located on OneDrive, or that uses any library located under the sketchbook. If I move the sketch/library to local hard-drive then everything compiles OK. Browsing/opening/editing/saving on OneDrive has no issues.
Looks like this happens only with Arduino 1.8 (tried 1.8.3 and 1.8.5), but Arduino 1.6.5 on the same machine doesn't have any issues and compiles everything without problems.
So what 1.8 have different from 1.6 that prevent it from compiling sketches/libraries on OneDrive? Is ther a workaround for this, or we'll have to wait till next release?