RBR50. Down load drops down to 0 while upload stays constant

What speeds do you pay for? 

What speeds do you get wired? 

What firmware is on your rbr50?

What modem/gateway is it connected to? 

How frequently does this happen? 

If it happens right away, does it happen if you hardwire a pc/laptop into your gateway? 

We need details to help. You didn't provide much past that you have an RBR50 and it slows down. Help us to help you.