2 bugs that have been around for quite a while. I’m on Mac Yosemite and Insync 1.2.13 but these have been the same on previous versions of OS and Insync.
My shared folder is on a NAS on the local network.
(1) If the NAS is mounted over SMB, Insync can’t deal with uploads properly. Uploading to Google Drive is a trickle (<1Mbit on a 12Mbit connection). At the same time the client downloads from the NAS with ~70Mbit. Makes it all but impossible to upload large files. When connecting the NAS via AFS instead of SMB, everything works as expected (fast upload, no exaggerated download from NAS). Behaviour is verified on 2 different installations. I have reported this twice already on this forum but never even got a reaction.
(2) Every once in a while Insync causes the internal Mac OS service “launchservicesd” to run amoc and eat 100% CPU. Only quitting and restarting Insync helps. I think this might mostly occurs if the network drive goes missing (i.e., is disconnected) and then reappears. Normally Insync handles that well except for (sometimes) sending launchservicesd on a rampage. Annoying, since every Insync-restart means “syncing metadata” for quite a while…