Cindysue-
Pluto loads and runs okay here, but it does seem to take longer to load than most, so don't give up too quickly. Until I see its splash screen, all I see is black. This was on my slowest Roku, a Streaming Stick 3600.
Edited to add:
After removing a channel, best practice is to restart** your Roku to clear its memory cache before reinstalling the channel. Without the restart you may not get a clean reinstall.
Depending on your Roku model and Roku version number you'll find the System restart option under either Settings > System > Power or under Settings > System. If you don't have sufficient control to use the menus, or if it is just more convenient, you can also restart by pulling the power plug for a short while, then plugging it back in.
**On a Roku TV with "Fast Start" enabled, turning the TV off/on only puts you in/out of a low power standby state, it does NOT give you a complete restart. Use the methods above.