What you got there is called "dead copper". You have isolated islands of GND pour, which aren't actually connected to anything.
I took an image and colored
some of the completely isolated GND spots:
This view really helps with the GND pour, you can get this view if you fill the board, go to 'layers' and only make the TOP/BOTTOM layer visible.
You seemed to have a lot of them in there.
I advice that you interconnect them by rerouting the traces as much as you can, but if you really can't manage that, you can use 1. vias or 2. jumper wire to connect the GNDs together.
All of the GND
must be connected together, atleast in single spot.
For example you can easily connect the 2 blue GNDs together simply by moving the one via. I bet you can connect all of those GNDs by rerouting. It's part of the fun and challenge.
When you're dealing with sensitive circuits(e.g. SMPS), you also need to take account that the common GND pour path isn't too long/thin for the specific components.
I'm not sure was there a tool in Eagle to recognize dead copper spots, I think I recall using it...
I hope this answered your question. Cheers.