Roku Express playback problems with 1080p videos, black screen, continuous loading

1080p videos in our channel (NET Nebraska) will not play on ROKU Express devices (failures occur on a 3930 Roku Express and 3931RW Roku Express+). The videos will play on Roku Ultra & Streaming Stick+ but on Roku Express devices there is only a black screen or continuous "loading" message,

To recreate, please visit our channel on a Roku Express and try to play the one of these videos in our featured row: "Great Plains Rail Tales", "Behind The Scenes at Antiques Roadshow Omaha", "The Land Will Outlive Us All", "And The Floods Came"

We have several videos in our feed that only have a 720p version and those play fine on ROKU Express but a majority of the videos in our feed have a 1080P version as well and none of those videos will play on the Express.

Here is a snippet from our feed that includes a 1080p video:

{"id":"50010910","title":"Super Sophomores","content":{"dateAdded":"2020-01-29T17:48:20.975210+00:00","videos":[{"url":"https://d34oa379y8jhb4.cloudfront.net/NETVOD/480/50010910.mp4","quality":"SD","videoType":"MP4"},{"url":"https://d34oa379y8jhb4.cloudfront.net/NETVOD/720/50010910.mp4","quality":"HD","videoType":"MP4"},{"url":"https://d34oa379y8jhb4.cloudfront.net/NETVOD/1080/50010910.mp4","quality":"FHD","videoType":"MP4"}],"captions":[{"url":"http://d1vmz9r13e2j4x.cloudfront.net/NET/misc/50010910.srt","language":"en-US","captionType":"CLOSED_CAPTION"}],"duration":232,"trickPlayFiles":[{"url":"https://d1vmz9r13e2j4x.cloudfront.net/NET/bif/50010910-fhd.bif","quality":"FHD"},{"url":"https://d1vmz9r13e2j4x.cloudfront.net/NET/bif/50010910-hd.bif","quality":"HD"},{"url":"https://d1vmz9r13e2j4x.cloudfront.net/NET/bif/50010910-sd.bif","quality":"SD"}],"language":"en-US","adBreaks":[]},"thumbnail":"http://d1vmz9r13e2j4x.cloudfront.net/NET/images/50010910_1080.jpg","shortDescription":"Meet the group of sophomores that are leading a young 2019-2020 Nebraska Women's Basketball team.","releaseDate":"2020-01-29T17:48:20.975210Z","longDescription":"Meet the group of sophomores that are leading a young 2019-2020 Nebraska Women's Basketball team.","tags":[],"genres":["sports"]}

Here are our encoding specifications:
Video Codec: H264 - MPEG-4 AVC (part 10), 1920x1080, 30fps
Audio Codec: MPEG AAC Audio (mp4a), 48000hz, 32bit

We opened a ticket with Roku support a few months ago and it was forwarded to their engineering team but the problem persists. Anyone have any advice?