Backup gets stuck at 100%

Two clients get to 100% of the file backup then get stuck there.
If I stop the service and restart it on the client side, it will work for a little while and then it will stop working again.
Urbackup Server 2.1.19, Ubuntu 16.04
UrBackup Client 1: 2.1.16, Debian GNU/Linux 7.5 (wheezy); Kernel 3.2.0-4-686-pae i686
UrBackup Client 2: 2.1.16, Debian GNU/Linux 7.7 (wheezy); Kernel 3.2.0-4-686-pae i686