Same thing here. I've had this in several campaigns so far.
It seems that countries, which start at very low funding, never increase their funding, ever. I don't think there are any external influences like alien bases at fault, but I can't be sure.
My theory is, that when current funding is below a certain threshold (maybe 10.000?), then any increase will be rounded down to zero.
So basically those countries are a lost cause from the beginning and there is nothing, that can be done about it.
Maybe.
Hopefully, I'm wrong.
Then again, you're not losing out on much money, anyway. Look at your other lowest funding countries. Even if they increase their contribution every month, it still never amounts to much. Typically, countries, that contribute big to your budget in the beginning, will do so throughout the game and vice versa. Unless you screw up big time, that will never change.