Maybe I am doing something wrong, but I just can’t add more than two folders to sync to any of my tablets. Any two, but at most two. Whenver I try to add a third I just can’t (clicking on “Add Folder” leads to a restarting that does nothing, or gets stuck forever; if I say to restart later, when I do, nothing happens either). I’ve seen this in a Nexus 7 with Android 4.4 and Asus TF201 with Android 4.1. I’ve rebooted the tablets and reinstall the Android app a couple of times, to no avail.
Solved. The problem was not a limit in the number of synced folders (I’ve added succesfully a bunch of others now) but the way I was interacting with what I find to be some non-intuitive and disconcerting features of the Android client (but I’ll open another thread for that). Sorry for the noise with this non-issue, then.