Channels are installed to your account, not a specific player. If you uninstalled then reinstalled on one, and the others don't check for updates during that time, they should be left alone. But if they update themselves while you have that channel uninstalled, they will be removed from the other devices as well. That's a good/bad thing with Roku players. Good in that once you've installed a channel on one device, it will appear on all the rest automatically. Just need to configure any logins necessary, as those are saved per device. Bad in that you remove it from one, it's removed from all. The only way around that is to have different Roku accounts for each player, but then you lose the good side of it.
Not meaning to get sidetracked, but I've noticed something after I got the 9.0 upgrade -- implying this is new as of 9.0, but it may pre-date -- when I added or removed an app from one Roku device, it removed it from the other devices right then. That is, I added an app to one device, went to another and lo, and behold, there it was. Then I removed the app from one, went directly to the other, and it was gone. So, unless I was experiencing some fluke, Roku now adds or removes from connected devices right then. When would wreak havoc on trying to remove/reinstall from one device, if it logged out of others.
I've not mentioned this before, but what you just said triggered it, so you might want to check and see if you experience the same thing.