I brought up this same issue in another thread under windows. The only way I could resolve it was to remove the account from insync and re-add it as new rather than an existing. When adding new, all the existing files are re-uploaded and sync without throwing errors. The issue has something to do with how insync file syncs for existing accounts. I’m guessing adding new rebuilds the file database where adding existing relies on the existing 1.5.x file database which is causing issues.