I confirm this problem too, this on Debian (/etc/debian_version = 9.0), insync 1.3.15, after the latest upgrade.
Headless seems to work okay, but not the GUI. Oddly enough, running the GUI as root brings it up alright. Below is a trace of running as a normal user.
$ insync start --no-daemon
INFO 2017-04-22 13:00:57,499 [__init__:info:1622] insync version: 1.3.15.36150
INFO 2017-04-22 13:00:57,500 [__init__:info:1622] client created
INFO 2017-04-22 13:00:57,500 [__init__:info:1622] unix socket server thread start
INFO 2017-04-22 13:00:57,501 [__init__:info:1622] starting client
INFO 2017-04-22 13:00:57,505 [__init__:info:1622] LinuxFSWatcher._start
INFO 2017-04-22 13:00:57,506 [__init__:info:1622] Inotify loop enter
GLib-GIO-Message: Using the 'memory' GSettings backend. Your settings will not be saved or shared with other applications.
INFO 2017-04-22 13:00:57,564 [__init__:info:1622] Syncing GDUser(id=u'118065391447553984249', email=u'xxxx@gmail.com', name=u'xxxx').
Fatal Python error: Segmentation fault
Thread 0x00007fc73fbb5700:
File “isyncd/linux/fswatch.py”, line 278 in _pull_loop
File “threading.py”, line 763 in run
File “threading.py”, line 810 in __bootstrap_inner
File “threading.py”, line 783 in __bootstrap
Thread 0x00007fc7403f6700:
File “SocketServer.py”, line 155 in _eintr_retry
File “SocketServer.py”, line 236 in serve_forever
File “isyncd/linux/portable/unix_socket_server_portable.py”, line 76 in __serve
File “threading.py”, line 763 in run
File “threading.py”, line 810 in __bootstrap_inner
File “threading.py”, line 783 in __bootstrap
Thread 0x00007fc751759700:
File “genericpath.py”, line 44 in isdir
File “isyncd/linux/fswatch.py”, line 179 in add_watch
File “isyncd/linux/fswatch.py”, line 155 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 156 in watch_tree
File “isyncd/linux/fswatch.py”, line 554 in watch
File “gevent/greenlet.py”, line 390 in run
Current thread 0x00007fc75cd08700:
File “main__insync.py”, line 117 in main
File “main__insync.py”, line 180 in
File “main.py”, line 128 in
File “”, line 6 in
Segmentation fault