It appears that there is a problem with the firmware or hardware of your Roku Express 4K+. Here are some methods you might try to remedy the problem:
Try resetting your Roku by unplugging it for at least 10 seconds, then plugging it back in and turning it on.
Examine your Roku for any accessible firmware updates. To accomplish this, navigate to Settings > System > System Update > Check it out right now.
Disable any unnecessary Roku features, such as "Fast TV Start," which allows your Roku to start up quickly but may also cause it to turn on at random. To turn this option off, navigate to Settings > System > Power > Fast TV Start.