controller.GetNodeAsync() sometimes returns null

[PaulHeitkemper]

i have a system where my nodes are running in sleep mode 5. They wake up every 200(ish) seconds. I have found that controller.GetNodeAsync() will often return null after it has attempted several messages to the node during the sleep. Even if I then hard-wire the sleep-request to ground to essentially make it permanently awake, I cannot communicate to the node.

Any ideas of a better way to handle that?