You are going to have to be more specific. What do you mean by “the not active RPi”? Are you using the webinterface, or the Cura plugin? What happens if you try? Do you get any error messages?
I am having a similar issue, however with 4.6. I have 3 printers, 3 RPIs. Two of the printers are Ender 3s I have to go into "manage printers" every time I want to change to another Ender3 and work directly with the Octoprint instance in order to connect to it.,..
The issue that I have is that I cannot read minds, nor access your computer to see what is going on. Please be more specific.
You have 3 instances of OctoPrint. Do these 3 instances have different names? Are they all showing up as different instances in the "Connect to OctoPrint" dialog? Can you add a screenshot?