Wyse C10LE Windows Server 2012 R2 RDP SessionTimeout

We've 20 C10LE Clients with new 8.1_27 Firmware.

The user sessions are irregular repeatedly ended the day.

debugfile:

07:45:16 RDP: Start session to 192.168.1.103
07:45:16 RDP: Connect to 192.168.1.103 ...
07:45:16 RDP: create network detection channel
07:45:16 RDP: create UDP transportation
12:50:13 RDP: UDP keepalive time out
12:51:20 TCP 0x2fa92ac: rexmt timedout, shift 8, 1693 ticks
12:51:20 RDP: pdu_recv_data: err code 110
12:54:08 RDP: Start session to 192.168.1.103
12:54:08 RDP: Connect to 192.168.1.103 ...
12:54:08 RDP: create network detection channel
12:54:08 RDP: create UDP transportation
13:50:06 mk_dhcp_msg[2160627]: sending Request
13:50:06 DHCP renew: 21600, 21600
13:50:06 DHCP rebind: 37800, 37800
13:50:06 DHCP lease: 43200, 43200
13:50:06 dhcp renew successfully: state = 0x0
13:51:54 RDP: UDP keepalive time out
13:52:49 TCP 0x2edd04c: rexmt timedout, shift 8, 1960 ticks
13:52:49 RDP: pdu_recv_data: err code 110
14:01:35 RDP: Start session to 192.168.1.103
14:01:35 RDP: Connect to 192.168.1.103 ...
14:01:35 RDP: create network detection channel

Does somebody has any idea?

Thank you! Sven