Okay, Thanks. They are.
I've noticed a new type of jpg files (created by crApple for their overpriced vision junk). It's a jpg contains two images (3d) with an extra exif property. Pic8 hasn't been updated to support these, and I'm not sure about its multiple hosts.
Poal has been updated though. So the expando fallback mirror are automatically converted to regular jpg.
That's interesting. I don't use an iphone though so should not apply to me.
Try to look at exif data in these images to see a pattern.
I had similar issues as you trying to create albums, and noticed that a corrupt/invalid image will display locally, but will create random album corruption (missing images and random errors when trying to share pic8 album link on Poal).
Try to first upload images individually. That way pic8 will throw an error when noticing a corrupt/invalid image, and thus showing you which one is causing the album issue.