In a situation where there is a render project with multiple render items, sometimes some nodes "drop off" from the render and go back in to the "watching" state. The rest of the machines continue the render. The problem is, that the ones that dropped off can't reconnect, unless after effects gets restarted.
I won't be able to help with this question because I don't have a lot of experience with render nodes and After Effects.
However, even folks with a lot of experience won't be able to help much either because you haven't provided enough information. Exact version number of AE (down to the last decimal), what sort of things are in your projects, network setup, render settings, and lots of other info would be useful. Heck, we don't even know if you're using Macs or Windows machines! FAQ: What information should I provide?