Video clips won't share in an iCloud Shared Album

I created a Shared Album in the Photos app on my desktop iMac of photos and videos I shot with my iPhone 15 and the video clips I've included will not appear in the iCloud Shared Album where I placed them. I tried the original 4K clips and also 1080 clips and they just won't show up. I was able to create a Shared Album on my iPad with two videos in it and the album and videos eventually showed up on my desktop Photos app, but it took a while. I have shared video clips in Shared Albums like this in the past with no problem. This seems to have started with the latest iOS (18.6.1) and OS (15.6.1). All of my software is up to date. Anyone else seeing this issue? Thanks for your help!