Consistently Poor Video Quality (Auto) Despite Very Fast Speeds

Hi. I'm seeing about 16 Megabytes / second internet speed when I run a internet speed test. According to the test: Your Internet connection should be able to handle multiple devices streaming HD videos, video conferencing, and gaming at the same time. Despite this, when I upload a 1080p video to Stream and when I hit the play button, it consistently auto plays at the lowest resolution (at most 480p, but typically 240p). I've tried encoding the video file multiple different ways, including at a low bit-rate (1 Mbps)  and a very high bit-rate (40 Mbps) but it never auto plays at 1080p or even 720p. If I click on some point in the play bar while the Quality is set to "Auto", it will adjust based on bandwidth and begin playing the video back at 1080p. And obviously, if I manually change the playback quality to HD, it will play the video in HD. But my viewers don't necessarily know this hack. From their perspective, they hit the Play button and the video just looks crappy and it's a terrible user experience. Why, if our internet speeds are considered very fast, does Stream automatically play an HD video at 480p or 240p? Why does it take me either manually changing the quality or clicking somewhere on the play bar to change the Quality settings and make the video playback at HD?