If your resources display a positive growth but you notice the number is not increasing, it's probably because your resource storage is at capacity. You can view your station's resource capacity by clicking the "Details" button on any of your Trading Post buildings inside your station. While your stored resources are above this limit, you will no longer produce new resources. However, using resource items or stealing from other stations will still add on to your resource balance as normal.
To check your resource capacity you can tap on the resource icons and amounts shown in the top left corner of the screen on the Space Station screen. (Just below your name in the top left.)
If you'd like to increase your resource capacity, just upgrade your existing Trading Posts or build new ones.