Product:
Planning Analytics 2.0.6
Microsoft Windows 2016 Terminal Server

Problem:
On new install of TM1 Architect on a Terminal Server, the list of TM1 instances is not showing up. They show up if you run TM1 architect direct on the TM1 server.

Solution:
Check Windows Firewall one both the Terminal Server and on your TM1 (PAL) server.
Go to Run from the start menu, enter wf.msc and press OK
Add a inbound rule that opens port 5495, 5498.
Save it as Cognos TM1 rule and check if it works again.

If you get a list of TM1 instances, but can not connect to them, then you miss the higher ports you have defined in TM1S.CFG
go back into Windows firewall, and add a port range like 12345-12360 to your cognos firewall rule.
Save and try again.

You need ports 5495, 5498 for TM1 Architect. 5895, 5898 is the Admin Server REST interface port (like HTTPPort for Tm1 servers). 5898 is when using TLS1.2
Then you need the ports you specify in TM1 applications – best to set a range like 12345-12360 then update in every TM1S.CFG file to unique values;
PortNumber=12345
HTTPportnumber=12346
ClientMessagePortNumber=12347

More Information:
https://www.ibm.com/support/knowledgecenter/en/SSD29G_2.0.0/com.ibm.swg.ba.cognos.tm1_inst.2.0.0.doc/c_tm1_inst_defaultvaluesfortm1installation.html
https://www.ibm.com/support/knowledgecenter/en/SSEP7J_11.1.0/com.ibm.swg.ba.cognos.inst_cr_winux.doc/c_reviewthedefaultsettings.html
https://www.ibm.com/support/knowledgecenter/en/SSD29G_2.0.0/com.ibm.swg.ba.cognos.tm1_inst.2.0.0.doc/c_paw_install_free_ports.html
http://cogknowhow.tm1.dk/archives/2055

Port 9300 is for Cognos Analytics (BI dispatcher).
Port 9510 is for TM1WEB and PMPSVC.
Port 5495,5498,5895,5898 is for TM1 Admin service.
Port 9012 is for the TM1 Agent.
Port 80 and 443 is for PAW or CA11 web-gateway ibmcognos.
There are other ports, but they are for communications between servers.