I have a Sansui 24" TV in our kitchen. (Model SLED2490) Originally, I installed the Roku Express without any issues (Roku Express was powered by the USB connection on the TV), but I decided to install the Roku Express 4K+. I immediately had issues from the time I powered the TV on. The screen began to blink from the Roku Logo to a black screen. (The Roku device was being powered by the USB on the TV.)
My solution: Use the USB block for power from a wall outlet to the Roku Express 4K+. My TV did not deliver enough power to this particular device using its internal USB. As mentioned before, I could power the Roku Express. I hope this helps some of the other people that have had similar issues, but no solution. Maybe it's possible that this may be a solution for other TV models that do not deliver enough power for the Roku device being installed.
I'm glad you discovered the solution. The TV's USB port is an "iffy" power source for Roku players. The USB 2.0 specification calls for 500 mA of power, but not all USB ports actually provide that level. And the Express 4K+ is certainly going to require more power than the older Express, as it's a much more powerful player.