Its not that they arent supported, they probably arent available for "Agent-Assisted" support (if they are lower end models, such as an Express), meaning you wont get a Roku employee interaction (chat/phone/email) - you have to use help/support articles and these community forums.
Neither of you mentioned your Roku model # or firmware version: Settings/System/About
It also might be useful to test your connection/speed: Settings/Network/Check connection What is the "Internet download speed" found?
Two things to try as a solution is to restore your default theme and choose a simple screensaver:
1) Restore default theme: Settings/Theme/Restore default theme/Restore
2) Choose simple screensaver: Settings/Theme/Screensaver/Roku digital clock/Set as default screensaver