Recently, I found that after I make some files locally, if I leave it aside like 10-20 minutes, I will find them online-only again. It is quite frustrating because it means that I have to constantly make things local in order to work on it. I checked my preference on Sync, it sets "available offline" for new files. I suspect, is there something called smart sync, which automatically make files online once your local storage is low? But this happens when my computer still have 260GB storage. So it's just weird.