Did it stop working you installed the second modbus contrib node? My first guess would be that the two conflict with each other.
If it is that then remove the other one. If you can't do it from Manage Palette (which may not be possible as the node names conflict), then open a command window, go into the folder where your flows file is (usually the folder is .node-red) and run npm remove node-red-contrib-modbus-ap...
I don't know exactly what it is called as it is off the screen. Then restart node red, refresh the browser page and see if it helps.
The "original", the first one is still working. The node just disappeared: dotted lines. I'm afraid, if I change anything in the flow and hit "deploy", it crashes.
And can it really be, that if I install node-red on a second raspi - they do interfere. They not even call the same modbus device
I didn't suggest that the two pi's conflict, I was suggesting that it may be the two modbus nodes, node-red-contrib-modbus and node-red-contrib-modbus-api that conflicted, but I have just tried it and it doesn't appear to be that.
Assuming that you have a conventional pi install of node red can you restart node red in a command window using node-red-stop node-red-start
And post the full startup output here please? That may tell us something. I presume you have already checked that restarting node-red and refreshing the browser page does not fix it.
In that case, don't stop it, just run node-red
that will attempt to startup another instance of node-red, which will fail as the port is already in use. It should not have any effect on the running system, but there is a good chance it will show us the problem.
Of course if you have a power glitch or similar then it will restart anyway, which could happen at a time when you are not available to fix it. At least if you try things when you are there then if there is a problem you have a chance of fixing it promptly.
