The problem is almost never your connection, but how Netflix sees it in that moment. The app might be experiencing latency spikes, packet loss, or just poor communication with its servers even though your overall speed is good. The actual bandwidth Netflix needs for the bitrate it's using also matters - it's not the same as the 300 Mbps you're paying for.
Try these things: first, restart your router and TV, wait a couple minutes. Then try connecting your TV with an ethernet cable if possible, that way you rule out wifi problems. In the Netflix app go to account settings, playback quality, and temporarily lower it to "Automatic" or even "Low" to see if it keeps happening. If the problem goes away it means Netflix detected that your network couldn't handle the bitrate you were requesting, even though it seems weird with that speed.
If nothing works, try closing all other apps using internet on your network and reset the Netflix app (uninstall and reinstall). Sometimes the cache is corrupted and forces weird retries. And yeah, Netflix is more sensitive than other services to this stuff, I'm not really sure why but it's well known.