I don't know if this has a bearing on your situation, but USB connections come in two power flavors: 500 mA and 1 A (Ampere). Some accessories won't work properly on just 500 mA. Some accessories need more than 1 Amp, which is why most outboard hard drives have a separate wall wart power supply.
Or...your hub is simply not working properly. (I'm assuming you are plugging in things which work correctly connected direct to the computer, but won't work connected to the hub).
It would help if you listed specific models of hub and accessories.
No, partly filling shouldn't make a difference, though real life can be weird sometimes.