Ground plane: is there a tool to identify choke points of a fragmented copper polygon in Eagle?
If your PC has a virus, it's best to nuke from orbit and rebuild it clean. Messing around looking for this and that, and hoping you've got everything, just isn't worth it.

Similarly, if you've turned your ground into a lace curtain by routing tracks through it, stop. Stop. Take a step back, several in fact.

If you're going to use a ground plane, keep it whole. Route nothing through it. 

You may need to add an extra layer to your stackup. Have you used power planes? They are almost always a waste of time and real estate. Ditch the power planes, and use those layers to move connections out of your ground plane.

If you have too few layers to dedicate one to ground, then don't use a ground plane. Use a ground grid on two layers, Manhattan style. This gives you a consistent way to get 'very good' ground and tracks systematically from anywhere to anywhere without cutting things up.