Backup videos in iCloud not in full quality

Hi everyone,

I have a problem with the quality of my videos in my icloud storage. I shot a 41sec 1080p video with my iPhone 6S, I have optimized storage enabled on my device..When I want to download the video from icloud.com in the Photos, it is only 5.5MB, when originally it was around 100MB I think. Have can I now recover the original full quality video?