So…
I simply moved the folder from .ix-apps/app_mounts/ to a folder inside another dataset.
I used the mv command, everything was kept intact (permissions, ownerships and dates).
I then modified the path in the app and everything started smoothly right after.
Cloudsync task is now properly configured and working!
Thanks all!
Would be a great feature to be able to lunch Cloud sync tasks on “hidden” dataset.