What @
HobeSoundDarryl said.
Plus, Wi-Fi routers use a radio signal to transmit to and from each device it is connected to. I would not be surprised if you have 30 or more devices connected to your router as so many devices these days have Wi-Fi. The router actually routes traffic to and from these devices, and just like rush hour traffic, sometimes speed can come to a crawl. If few devices are currently requesting band width (a slice of the pie), then those that are probably will get it. But if many devices are requesting band width simultaneously, you can get a traffic jam and signal strength can drop so low as to cause temporary disruptions in streaming. Also, since the router uses radio signals, those signals can be interfered with by other devices. So Wi-Fi can be problematic in some cases.
Ethernet on the other hand, is not as susceptible to interference or band width, is much more reliable, and much more stable. If you are currently experiencing a lot of interruptions and problems when streaming TV video, then ethernet might be the solution. It only takes around 25 Mbps of speed to reliably stream 4K TV, but if the speed fluctuates a lot then you can have issues, and ethernet is more likely to keep the fluctuations under control than Wi-Fi. If you have 100+ Mbps internet speed, Wi-Fi might work fine, but a bad or old router can even have trouble with that if the total demand leaves less than 25 Mbps available for your streaming box.
I recommend running ethernet to all streaming boxes if possible. Alternatively, get a newer router that can handle traffic more efficiently. Also make sure you internet speed is high enough to support your devices.