Have you tested what @cpt_paranoia has suggested with a cat5e? That’s the best bet to know if either router or TV or MyCloud is abnormal.
100Mbps N rated wifi router or homeplug shouldn’t have stuttering with your normal vids unless your vids have very high bitrate or your network is congested heavily. I can stream 10GB 1080p from home to another TV located at someone else’s place without stuttering, just few seconds initial buffers (MyCloud->Internet->Wifi->SmartPhone->Cast->TV). This also works from a 4G network so I don’t think your stuttering issue is solely related to MyCloud.
To test your wifi, there’s several apps on mobile/pc. I’m using mobile Wifi Analyzer to check for congested channels. My area both 2.4GHz and 5GHz are like hotcakes overlapping. If you’re living around one like mine, choose the least overlapping channel. Note that other non-ssid broadcasting devices could also be the culprit i.e. cordless phones and baby monitors. Replace those with 1.9GHz or 900MHz if possible (if they belong to your neighbours, get them a new one 
).
