This usually indicates a failed device (memory issue). If under warranty, would just return or replace.
If past warranty (1 year replacement), you can try replacing the power adapter and performing a Factory Reset on the suspect device. (Press and hold reset button for 30+ seconds).
Other things to try (depending on Roku model number) is to remove the SD card if equipped and try using a default theme and screensaver.
If you have a Streaming Stick (these seem to be the most affected), try using a power adapter at the wall if currently using TV USB power port. (Use 5volt 1amp adapter).
The other ones that seem affected are the Ultra. Other than the SD card and power supply replacement, I haven't seen anything else to remedy.
In most of the cases, it does seem to be a bad or underpowered device that causes this issue.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941