I had an issue with the behaviour of Insync selective sync.
I had a folder A with selective sync activated in my laptop. Then, I created a subfolder B inside folder A and uploaded 100000 files with a total size of 500 GB to folder B on my desktop computer. Immediately after the upload started, I refreshed the folder tree in folder A and disabled B folder from Insync selective sync in my laptop as I did not have 500 GB free in my laptop hard drive. After a while, I checked my laptop and Insync was complaining that was no space left in the laptop hard drive for downloading folder B. Then, I checked folder B in my laptop hard drive and realised that Insync was downloading all the files in folder B although selective sync was disabled for that folder.
To workaround this issue, I closed Insync and delete folder B in my laptop, but it resumed trying to download the all files of folder B after restarting Insync although this time was skipping and giving the error “folder B does not exists” for each file. Then, I closed all the errors to avoid the retry of files downloading by accident as the (de)syncing of folder B took several hours.
I have Insync v1.5.5. both my laptop and my desktop computer.
I would really recommend changing Insync software behaviour so it cancels syncing downloads to a folder when syncing of this folder is disabled by selective sync, or adding the option to not activate syncing by default on newly created subfolders.