Firstly, a node should never crash node-red - so regardless of what you are doing to make it happen, you should raise this as an issue on the repository (in fact it may already be a raised issue)
For the short term, I would check that the IP is visible from within the node-red (for example, if you are running in docker, then it probably wont be or will be a different IP). Basically, as you are creating a modbus server, the IP and PORT it binds to must be available to the OS (be that a docker guest or a OS on the metal) where node-red is executing. That includes firewalls.
