Hello Jim Davies,
Tap Settings > Wi-Fi on all of your devices. Check that Wi-Fi is on and you have an internet connection.
Tap Settings > [your name] > iCloud > Photos. Make sure Upload to My Photo Stream is turned on. If you don’t see this option, turn on iCloud Photos to keep your photos and videos in iCloud instead.
On the device that captured the photo that you’re looking for, close the Camera app. (Nothing uploads to My Photo Stream until you do.)
See if your iOS device is below 20% battery power. If it is, My Photo Stream disables itself temporarily to save battery life.
This should fix your issue.