I noticed others have had this issue, but I have some files selected as "online only" via smart sync and they are still taking up space on my hard drive, causing my mac to tell me I'm running out of hard drive space. It's happening with multiple files, but I've included screen shots for one as an example. I'm running MacOS High Sierra 10.13.6, and dropbox v59.4.93.
As you can see in the first screenshot, my Mac HD says my largest file is "CC IBD Training.MOV" stored in "Next Steps-->Citygroups-->Videos" folder.
"Large Files" stored on my hard driveNow if you look at this screenshot, I pull up the folder Next Steps-->Citygroups-->Videos. The whole folder is selected as "online only" as is the "CC IBD Training" video. Strangely, the other 2 videos in this folder do not show up on my hard drive, but "CC IBD Training" still says it's stored on my hard drive, as indicated above.
Same file here indicated to be "online only"What can I do about this? As you can see, I'm low on hard drive space and as a result cannot install MacOS Mojave.