Could this be related to the issue where 0 byte files would cause sync to stop. I haven’t tested on Android for a while (will do as soon as I get a moment). Not sure if that bug was identified/addressed, but, if not, it would be great to at least get a test up that checks for behaviour of 0 byte files on sync.
(When I last tested, I could reliably cause sync to hang by including a 0 byte file and get it to restart by removing it.)
(And apologies in advance if this has been addressed and if I missed it.)