I don't know what does it means, it seems something related to the server status.
From the catch node, I get this output
TypeError: Cannot read property 'getMachineState' of undefined at Object._inputCallback (/opt/node-red/node_modules/node-red-contrib-modbus/modbus/maps/modbus-flex-write.js:52:5) at Object.Node._emitInput (/opt/node-red/node_modules/@node-red/runtime/lib/nodes/Node.js:199:18) at Immediate._onImmediate (/opt/node-red/node_modules/@node-red/runtime/lib/nodes/Node.js:179:33) at processImmediate (internal/timers.js:439:21)
What version of node-red and nodejs are you using. For the latter, use node -v
If that is V12, 14, or 16 then that should be ok. If you are using a recent version of node red then probably best to post an issue on the node's GitHub page.