Devices only see server when Firewall is dropped

[KnightCat83]

Have you tried adding a rule to the firewall in Windows? Since turning it off lets everything work, I would guess that the issue is directly in the configuration of that firewall. I’ve quoted the related part of another thread:

@SunnyDays

Navigate to Control Panel, System and Security and Windows Firewall , or simply type into the Windows Start Menu search box: wf.msc

• [Updated 4-11-19]: Do this for both Inbound Rules and Outbound Rules in the left pane (so twice)
• Under Actions , select New Rule
• Select Port and click Next
• Select TCP protocol and the Specific local port number of 32400 and click Next
• Select Allow the connection in the next window and click Next
• Select all 3 rules, Domain, Private and Public and click Next
• Name the rule something like Plex TCP Allow and click Finish
  The 32400 Port will now be open. Also, be sure to have, under the properties of the port rule ‘Plex TCP Allow’:
• General tab > Enabled (ticked), Action = Allow the connection,
• Protocols and ports > Protocol type = TCP,
• Advanced > Profiles (all ticked), Edge traversal = DISABLED
  (So just make sure they are set as above)