WP7607 - SSH connection over USB cable drops without clear reason

Hi,
I use a WP7607 with Legato 18.10.2 and Yocto 2.2 on a custom board.
The custom board is connected to my host Linux PC with a USB cable.
When I use the Terminal in Developer Studio to create an SSH connection over this USB cable, I can run different commands on my target.
Sometimes this SSH connection drops without a clear reason (after a few hours).
The log file indicates:
Mar 1 12:53:07 swi-mdm9x28 daemon.info dnsmasq-dhcp[1353]: DHCPREQUEST(ecm0) 192.168.2.3 fa:0c:09:c6:a5:1f
Mar 1 12:53:07 swi-mdm9x28 daemon.info dnsmasq-dhcp[1353]: DHCPNAK(ecm0) 192.168.2.3 fa:0c:09:c6:a5:1f lease not found
Mar 1 12:53:20 swi-mdm9x28 daemon.info dnsmasq-dhcp[1353]: DHCPDISCOVER(ecm0) 192.168.2.3 fa:0c:09:c6:a5:1f
Mar 1 12:53:20 swi-mdm9x28 daemon.info dnsmasq-dhcp[1353]: DHCPOFFER(ecm0) 192.168.2.3 fa:0c:09:c6:a5:1f
Mar 1 12:53:20 swi-mdm9x28 daemon.info dnsmasq-dhcp[1353]: DHCPREQUEST(ecm0) 192.168.2.3 fa:0c:09:c6:a5:1f
Mar 1 12:53:20 swi-mdm9x28 daemon.info dnsmasq-dhcp[1353]: DHCPACK(ecm0) 192.168.2.3 fa:0c:09:c6:a5:1f HostPC
Mar 1 12:53:21 swi-mdm9x28 authpriv.info dropbear[1623]: Exit (root): Exited normally
Mar 1 12:53:22 swi-mdm9x28 authpriv.info dropbear[25106]: Child connection from 192.168.2.3:52398

Greetings,
annaertd

You may try disable network manager and modem manager and see if problem is solved.