Video stream specially from YouTube can fail due to restrictions on their platform. It can be because too many requests have been done for a video in which case it is necessary to wait until the restriction is gone. Other than that video streaming will likely not fail in other platforms unless they implement their own restrictions on the request. When the issue is performance it is because blender doesn't handle video decoding efficiently. It is a common issue since a very long time that Blender doesn't support GPU decoding which can affect performance severely specially when choosing high resolution streams. It all depends on your CPU. We also have done optimizations to avoid slowing down your viewport as much as possible when playing a video.