The game warns me that Starbase in Halvam system is not connected to the Trade Network even though I see a direct connection between systems on the map. See the image below.
Interestingly, there are 2 other Starbases (in Sym and Syldus) that don't look connected as well (their icon is red), but the game does not warn they are not connected.
Why is this so and how to get Halvam connected with the Trade Network?
Best Answer
When you claim systems with trade hubs at the end of a war, which it looks like these were, the game does not automatically connect them to your trade network. It's up to you to connect them manually. (If you can; in some cases you might end up with odd borders where systems are isolated from your empire and can't be linked.)
As for the other two systems, my initial guess would be that the game doesn't bother to notify you if no trade is actually being collected by those starbases.