Can’t play videos uploaded on iCloud Photo Sharing folders

I am trying to upload some videos from my Camera Roll to an iCloud Photo Sharing folder, but as I do that, I seem to be unable to play the videos afterwards. There’s a low-res preview of the video’s thumbnail, and touching the play button brings out a circle with an exclamation mark ⚠ followed by a message saying ”Download Error.” as you can see on the following screenshots:

I have tried uploading them both from cellular data and from a Wifi connection, I’ve tried deleting them from the shared folder and reuploading it, I’ve tried force closing the app, and (of course) I’ve tried turning my phone off and on again.

However, previously uploaded videos can be played successfully, as opposed to recently uploaded videos.

What is causing this? Is there any way to fix this?

[Using an iPhone 6, model MQ3X2CL/A, iOS 11.2.6 (15D100)]