Third party firewall
If there is a third-party firewall software or anti virus (eg Avast, AVG, etc.) with own firewall settings running on Primary Machine, then this can prevent spacedesk discovery and connection.
Please ensure that C: \ Windows \ System32 \ spacedeskService.exe is allowed through the firewall software or the spacedesk TCP / IP network protocol port is opened. spacedesk is using TCP port 28252.
In case there is a McAfee antivirus or firewall software installed, try the settings below or just disable it to check if spacedesk Viewer app can discover the Primary Machine. There is a known connection issue on spacedesk with McAfee software where after a few minutes of connectivity, McAfee on Windows is known to randomly kill and prevent network connections without informing the user.
Try to add spacedeskService in McAfee Firewall settings, click Ports and System Services then click the Add button.
System Service Name: spacedeskService
Local TCP/IP Ports: 28252
Local UDP Ports: 28252
Please ensure that the Windows Firewall settings is correct. For details please check chapter Setup Primary Machine – Verify if setup was successful .