You have just applied SU5 patch to your LDMS 2016 core server.
After installing the patch, you are not able to successfully initiate legacy remote control sessions using the standalone version of the component (isscntr.exe) that can be installed through the ENURCSetup.exe package in IIS.
The viewer always gets stuck on the following message "The remote computer has been contacted using TCP"
This is a known issue that is currently being investigated by our engineering team. The issue is related with an outdated version of the "isscntr.exe" file being shipped with SU5.
A specific bug report has been opened for this issue: Defect 360699:Outdated version of isscntr.exe contained in ENURCSetup.exe in LDMS 2016 SU5 cause RC session to fail to initiate when attempting to remotely control Windows computers
A fix will be made available in 2016.3 release.
Customers experiencing the issue are encouraged to use the HTML5 remote control feature until the fix is made available