After upgrading to version 2.6.6, I am not able to sync any collection, neither individually nor using the new “Sync All” button: the app gets stuck showing “LOADING Sending updates to server …”. The “piano keys” keep moving, so it is probably not dead, but there is no way to stop it other than to restart the app.
Update 1: I find that downloading collections does not work either, getting stuck on “Generating download…”.
Update 2: Trying “Sync All” (Danish from Spanish) about one hour later, it got stuck on “Updating collection undefined (1/2)…”. After a restart, the “Sync All” button was gone. I can’t really tell whether the sync was actually performed or not.