What Roku model and model number is it (Settings > System > About)?
How are you powering your Roku -- plugged into the USB port on your tv, or into a power adapter connected to your house power? Many tv USB ports don't supply the amperage needed to power a Roku reliably. If this is what you are doing, try connecting it into the USB power adapter that came with it, plugged directly to your house power. If you don't have the adapter, any USB power supply, such as you may have from an old phone, is okay as long as its output is rated at 5 volts and at least 1 amp (check the writing on the adapter - you may need a magnifying glass).
If you're already powering via USB adapter plugged into your house power, see if a different adapter helps.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T